Dallas DS1923-F5 Hygrochron temperature/humidity logger ibutton with 8kb data log memory Datasheet

DS1923
Hygrochron Temperature/Humidity Logger
iButton with 8kB Data Log Memory
www.maxim-ic.com
SPECIAL FEATURES
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iButton DESCRIPTION
Digital Hygrometer Measures Humidity with 8-Bit
(0.6%RH) or 12-Bit (0.04%RH) Resolution
Operating Range: -20 to +85°C; 0 to 100%RH
(see Safe Operating Range)
Automatically Wakes Up, Measures Temperature
and/or Humidity and Stores Values in 8kB of
Datalog Memory in 8- or 16-Bit Format
Digital Thermometer Measures Temperature with
8-Bit (0.5°C) or 11-Bit (0.0625°C) Resolution
Temperature Accuracy Better than ±0.5°C from
-10°C to +65°C with Software Correction
Built-in Humidity Sensor for Simultaneous
Temperature and Humidity Logging
Capacitive Polymer Humidity-Sensing Element
Hydrophobic Filter Protects Sensor Against Dust,
Dirt, Contaminants, and Water
Droplets/Condensation
Sampling Rate from 1s up to 273hrs
Programmable Recording Start Delay After
Elapsed Time or Upon a Temperature Alarm Trip
Point
Programmable High and Low Trip Points for
Temperature and Humidity Alarms
Quick Access to Alarmed Devices Through
1-Wire® Conditional Search Function
512 Bytes of General-Purpose Memory Plus 64
Bytes of Calibration Memory
Two-Level Password Protection of All Memory
and Configuration Registers
Communicates to Host with a Single Digital Signal
at Up to 15.4kbps at Standard Speed or Up to
125kbps in Overdrive Mode Using 1-Wire Protocol
Individually Calibrated in a NIST-Traceable
Chamber
Calibration Coefficients for Temperature and
Humidity Factory Programmed into Nonvolatile
(NV) Memory
The DS1923 temperature/humidity logger iButton® is a
rugged, self-sufficient system that measures
temperature and/or humidity and records the result in
a protected memory section. The recording is done at
a user-defined rate. A total of 8192 8-bit readings or
4096 16-bit readings taken at equidistant intervals
ranging from 1s to 273hrs can be stored. In addition to
this, there are 512 bytes of SRAM for storing
application-specific information and 64 bytes for
calibration data. A mission to collect data can be
programmed to begin immediately, or after a userdefined delay or after a temperature alarm. Access to
the memory and control functions can be passwordprotected. The DS1923 is configured and
communicates with a host-computing device through
the serial 1-Wire protocol, which requires only a single
data lead and a ground return. Every DS1923 is
factory-lasered with a guaranteed unique 64-bit
registration number that allows for absolute
traceability. The durable stainless-steel package is
highly resistant to environmental hazards such as dirt,
moisture, and shock. Accessories permit the DS1923
to be mounted on almost any object, including
containers, pallets and bags.
F5 MICROCAN
APPLICATIONS
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16.25
17.35
GND
Front Side Brand
A1
All dimensions are
shown in millimeters.
®
41
000000FBC52B
1-Wire®
HygrochronTM
PACKAGE
F5 iButton
1-Wire and iButton are registered trademarks and Hygrochron is
a trademark of Dallas Semiconductor, Corp., a wholly owned
subsidiary of Maxim Integrated Products, Inc.
®
®
ORDERING INFORMATION
TEMP RANGE
-20°C to +85°C
0.51
IO
Temperature and Humidity Logging in Food
Preparation and Processing
Transportation of Temperature- and HumiditySensitive Goods, Industrial Production
Warehouse Monitoring
Environmental Studies/Monitoring
PART
DS1923-F5
5.89
Back Side Brand
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REV: 120507
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data log Memory
DS1923 ABSOLUTE MAXIMUM RATINGS
IO Voltage to GND
IO Sink current
Operating Temperature and Humidity Range
-0.3V, +6V
20mA
-20°C to +85°C, 0%RH to 100%RH
(See Safe Operating Range Chart)
-40°C to +85°C, 0%RH to 100%RH
(See Safe Operating Range Chart)
Storage Temperature and Humidity Range
This is a stress rating only and functional operation of the device at these or any other conditions above those
indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating
conditions for extended periods of time may affect reliability.
DS1923 ELECTRICAL CHARACTERISTICS
(VPUP = 3.0V to 5.25V, TA = -20°C to +85°C)
PARAMETER
IO Pin General Data
1-Wire Pullup
Resistance
Input Capacitance
Input Load Current
High-to-Low Switching
Threshold
Input Low Voltage
Low-to-High Switching
Threshold
Switching Hysteresis
Output Low Voltage
SYMBOL
RPUP
CONDITIONS
TYP
(Notes 1, 2)
UNITS
2.2
kΩ
800
10
pF
µA
3.2
V
0.3
V
(Note 3)
IO pin at VPUP
VTL
(Notes 4. 5)
VIL
(Notes 1, 6)
VTH
(Notes 4, 7)
0.7
3.4
V
VHY
VOL
(Note 8)
At 4mA (Note 9)
Standard speed, RPUP = 2.2kΩ
Overdrive speed, RPUP = 2.2kΩ
Overdrive speed, directly prior to
reset pulse; RPUP = 2.2kΩ
0.09
N/A
0.4
V
V
(Note 10)
0.6
tREC
Rising-Edge Hold-off
Time
tREH
100
6
MAX
CIO
IL
Recovery Time
(Note 1)
0.4
Standard speed
Overdrive speed, VPUP > 4.5V
Overdrive speed (Note 11)
IO Pin, 1-Wire Reset, Presence Detect Cycle
Standard speed, VPUP > 4.5V
Reset Low Time
Standard speed (Note 11)
tRSTL
(Note 1)
Overdrive speed, VPUP > 4.5V
Overdrive speed (Note 11)
Standard speed, VPUP > 4.5V
Presence-Detect High
tPDH
Standard speed (Note 11)
Time
Overdrive speed (Note 11)
Standard speed, VPUP > 4.5V
Presence-Detect Fall
Time
tFPD
Standard speed
(Note 12)
Overdrive speed
Standard speed, VPUP > 4.5V
Standard speed (Note 11)
Presence-Detect Low
tPDL
Overdrive speed, VPUP > 4.5V
Time
(Note 11)
Overdrive speed (Note 11)
Standard speed, VPUP > 4.5V
Presence-Detect
Sample Time
tMSP
Standard speed
(Note 1)
Overdrive speed
Timeslot Duration
(Note 1)
MIN
tSLOT
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5
2
µs
5
2.0
65
8
9.5
µs
µs
480
690
48
70
15
15
2
1.5
1.5
0.15
60
60
720
720
80
80
60
63.5
7
5
8
1
240
287
7
24
7
65
71.5
8
28
75
75
9
µs
µs
µs
µs
µs
PARAMETER
IO Pin, 1-Wire Write
Write-0 Low Time
(Note 1)
Write-1 Low Time
(Notes 1, 13)
IO Pin, 1-Wire Read
Read Low Time
(Notes 1, 14)
Read Sample Time
(Notes 1, 14)
Real-Time Clock
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
SYMBOL
CONDITIONS
MIN
TYP
MAX UNITS
tW0L
tW1L
tRL
tMSR
Accuracy
Frequency Deviation
Temperature Converter
Conversion Time
RH Range
RH Accuracy and
Interchangeability
RH Nonlinearity
RH Hysteresis
RH Repeatability
Long-Term Stability
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
Note 10:
Note 11:
Note 12:
Note 13:
Note 14:
Note 15:
Note 16:
60
120
6
12
7.5
5
1
12
15 - ε
1.95 - ε
5
1
tRL + δ
tRL + δ
15 - δ
1.95 - δ
15
1.95
-3
+3
-20°C to +85°C
-300
+60
8-bit mode (Note 15)
16-bit mode (11 bits)
30
240
75
600
Standard speed
Overdrive speed
Standard speed
Overdrive speed
+25°C
ΔF
tCONV
Thermal Response
τRESP
Time Constant
Conversion Error
Without Software
Δϑ
Correction
Conversion Error With
Δϑ
Software Correction
Humidity Converter (Note 30)
Humidity Response
τRH
Time Constant
RH Resolution
Standard speed
Overdrive speed, VPUP > 4.5V
(Note 11)
Overdrive speed (Note 11)
Standard speed
Overdrive speed
iButton package (Note 16)
µs
µs
µs
µs
min./
month
PPM
ms
130
s
(Notes 15, 17, 18, 19)
See Temperature
Accuracy Graphs
°C
(Notes 15, 17, 18, 19)
See Temperature
Accuracy Graphs
°C
30
s
Slow moving air (Note 20)
(Note 21)
(Note 22)
With software correction
(Notes 18, 19, 23, 24, 25)
With software correction (Note 18)
(Notes 26, 27)
(Note 28)
At 50%RH (Note 29)
8
0.64
0
12
0.04
12
0.04
100
bits
%RH
%RH
±5
%RH
<1
0.5
±0.5
<1.0
%RH
%RH
%RH/y
System requirement.
Maximum allowable pullup resistance is a function of the number of 1-Wire devices in the system and 1-Wire recovery times. The
specified value here applies to systems with only one device and with the minimum 1-Wire recovery times. For more heavily
loaded systems, an active pullup such as that found in the DS2480B may be required.
Capacitance on the data pin could be 800pF when VPUP is first applied. If a 2.2kΩ resistor is used to pull up the data line 2.5µs
after VPUP has been applied, the parasite capacitance does not affect normal communications.
VTL, VTH are a function of the internal supply voltage.
Voltage below which, during a falling edge on IO, a logic '0' is detected.
The voltage on IO needs to be less or equal to VILMAX whenever the master drives the line low.
Voltage above which, during a rising edge on IO, a logic '1' is detected.
After VTH is crossed during a rising edge on IO, the voltage on IO has to drop by VHY to be detected as logic '0'.
The I-V characteristic is linear for voltages less than 1V.
The earliest recognition of a negative edge is possible at tREH after VTH has been previously reached.
Highlighted numbers are NOT in compliance with the published iButton standards. See comparison table below.
Interval during the negative edge on IO at the beginning of a presence detect pulse between the time at which the voltage is 90%
of VPUP and the time at which the voltage is 10% of VPUP.
ε represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to VTH.
δ represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to the input high threshold of the bus
master.
To conserve battery power, use 8-bit temperature logging whenever possible.
This number was derived from a test conducted by Cemagref in Antony, France, in July of 2000.
http://www.cemagref.fr/English/index.htm Test Report No. E42.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Note 17:
Note 18:
Note 19:
Note 20:
Note 21:
Note 22:
Note 23:
Note 24:
Note 25:
Note 26:
Note 27:
Note 28:
Note 29:
Note 30:
For software corrected accuracy, assume correction using calibration coefficients with calibration equations for error
compensation.
Software correction for humidity and temperature is handled automatically using the 1-Wire Viewer Software package available
at: http://www.ibutton.com.
WARNING: Not for use as the sole method of measuring or tracking temperature and/or humidity in products and articles that
could affect the health or safety of persons, plants, animals, or other living organisms, including but not limited to foods,
beverages, pharmaceuticals, medications, blood and blood products, organs, flammable, and combustible products. User shall
assure that redundant (or other primary) methods of testing and determining the handling methods, quality, and fitness of the
articles and products should be implemented. Temperature and/or humidity tracking with this product, where the health or safety
of the aforementioned persons or things could be adversely affected, is only recommended when supplemental or redundant
information sources are used. Data logger products are 100% tested and calibrated at time of manufacture by Dallas
Semiconductor/Maxim to ensure that they meet all data sheet parameters, including temperature accuracy. User shall be
responsible for proper use and storage of this product. As with any sensor-based product, user shall also be responsible for
occasionally rechecking the temperature accuracy of the product to ensure it is still operating properly.
Response time is determined by measuring the 1/e point as the device transitions from 40 to 90%RH or 90 to 40%RH, whichever
is slower. Test was performed at 5L/min airflow.
All DS1923 humidity measurements are 12-bit readings. Missioning determines 8-bit or 16-bit data logging. Battery lifetime is the
same no matter what RH resolution is logged.
Reliability studies have shown that the device survives a minimum of 1000 cycles of condensation and drying, but this product is
not guaranteed for extended use in condensing environments.
Software corrected accuracy is accomplished using the method detailed in the Software Correction Algorithm for Temperature
section of this data sheet.
Every DS1923 Device is measured and calibrated in a controlled, NIST-traceable RH environment.
Higher accuracy versions may be available. Contact the factory for details.
If this device is exposed to a high humidity environment (>70%RH), and then exposed to a lower RH environment, the device will
read high for a period of time. The device will typically read within +0.5%RH at 20%RH, 30 minutes after being exposed to
continuous 80%RH for 30 minutes.
All capacitive RH sensors can change their reading depending upon how long they have spent at high (>70%RH) or low RH
(<20%RH). This effect is called saturation drift and can be compensated through software, as described in the Software
Saturation Drift Compensation section of this data sheet.
Individual RH readings always include a noise component (repeatability). To minimize measurement error, average as many
samples as is reasonable.
Like all relative humidity sensors, when exposed to contaminants and/or conditions toward the limits of the safe operating range,
accuracy degradation can result (see Safe Operating Range chart). For maximum long-term stability, the sensor should not be
exposed or subjected to organic solvents, corrosive agents (strong acids, SO2, H2SO4, CI2 ,HCL, H2S, etc.) and strong bases
(compounds with PH greater than 7). Dust settling on the filter surface does not affect the sensor performance except to possibly
decrease the speed of response.
For more information on the RH sensor’s tolerance to chemicals visit:
http://content.honeywell.com/sensing/prodinfo/humiditymoisture/technical/c15_144.pdf
All humidity specifications are determined at +25°C except where specifically indicated.
Parameter
Name
tSLOT (incl. tREC)
tRSTL
tPDH
tPDL
tW0L
1)
Standard Values
Standard Speed
Overdrive Speed
Min
Max
Min
Max
61µs
(undef.)
7µs
(undef.)
480µs
(undef.)
48µs
80µs
15µs
60µs
2µs
6µs
60µs
240µs
8µs
24µs
60µs
120µs
6µs
16µs
DS1923 Values
Standard Speed
Overdrive Speed
Min
Max
Min
Max
65µs1)
(undef.)
9.5µs
(undef.)
690µs
720µs
70µs
80µs
15µs
63.5µs
2µs
7µs
60µs
287µs
7µs
28µs
60µs
120µs
7.5µs
12µs
Intentional change, longer recovery time requirement due to modified 1-Wire front end.
PHYSICAL SPECIFICATION
Size
Weight
Safety
See mechanical drawing
Ca. 5.0 grams
Meets UL#913 (4th Edit.); Intrinsically Safe Apparatus,
approval under Entity Concept for use in Class I,
Division 1, Group A, B, C, and D Locations
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Safe Operating Range
Storage Only
Humidity (%RH)
100
80
60
40
20
Safe Operating Zone
0
-40
-20
0
20
40
60
80
Temperature (°C)
DS1923 Temperature Accuracy
Uncorrected Max Error
Uncorrected Min Error
SW Corrected Max Error
SW Corrected Min Error
2.0
DS1923: Error (°C)
1.5
1.0
0.5
0.0
-0.5
-1.0
-20
-10
0
10
20
30
40
Temperature (°C)
NOTE: The graphs are based on 11-bit data.
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50
60
70
80
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
8-Bit Min. Product Lifetime (years)
Minimum Lifetime vs. Temperature, Slow Sampling Temperature Only
Every Minute
Every 3 Min.
Every 10 Min.
Every 60 Min.
No Samples
Osc. Off
10
9
8
7
6
5
4
3
2
1
0
-20
-10
0
10
20
30
40
50
60
70
80
11-Bit Min. Product Lifetime
(years)
DS1923: Temperature (°C)
Every Minute
Every 3 Min.
Every 10 Min.
Every 30 Min.
Every 60 Min.
Every 300 Min.
No Samples
Osc. Off
10
9
8
7
6
5
4
3
2
1
0
-20
-10
0
10
20
30
40
50
DS1923: Temperature (°C)
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60
70
80
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
8-Bit Min. Product Lifetime (days)
Minimum Lifetime vs. Temperature, Fast Sampling Temperature Only
Every Second
Every 3 Sec.
Every 30 Sec.
Every 60 Sec.
Every 10 Sec.
350
300
250
200
150
100
50
0
-20
-10
0
10
20
30
40
50
60
70
80
11-Bit Min. Product Lifetime
(days)
DS1923: Temperature (°C)
Every Second
Every 3 Sec.
Every 10 Sec.
Every 30 Sec.
Every 60 Sec.
100
80
60
40
20
0
-20
-10
0
10
20
30
40
50
DS1923: Temperature (°C)
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60
70
80
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Minimum Lifetime vs. Temperature, Slow Sampling, Temperature with Humidity
Every Minute
Every 3 Min.
Every 10 Min.
Every 60 Min.
No Samples
Osc. Off
8-Bit Temp. plus Humidity Min.
Product Lifetime (years)
10
9
8
7
6
5
4
3
2
1
0
-20
-10
0
10
20
30
40
50
60
70
80
DS1923: Temperature (°C)
8-Bit Temp. plus Humidity Min.
Product Lifetime (days)
Minimum Lifetime vs. Temperature, Fast Sampling, Temperature with Humidity
Every Second
Every 3 Sec.
Every 30 Sec.
Every 60 Sec.
Every 10 Sec.
350
300
250
200
150
100
50
0
-20
-10
0
10
20
30
40
50
DS1923: Temperature (°C)
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60
70
80
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Minimum Product Lifetime vs. Sample Rate (Temperature Only)
8-Bit Min. Product Lifetime (years)
0°C
40°C
60°C
75°C
85°C
10
1
0.1
0.01
0.01
0.1
1
10
100
DS1923: Minutes between Samples
NOTE: With humidity logging activated, the lifetime is reduced by less than 11% for sample rate of 3 minutes and
slower and by a maximum of 20% for sample rate of 1 minute and faster.
11-Bit Min. Product Lifetime (years)
0°C
40°C
60°C
75°C
85°C
10
1
0.1
0.01
0.001
0.01
0.1
1
10
100
DS1923: Minutes between Samples
NOTE: With humidity logging activated, the lifetime is reduced by a maximum of 4%. The incremental energy
consumed by humidity logging is independent of the humidity logging resolution.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
COMMON iButton FEATURES
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Digital Identification and Information by Momentary Contact
Unique Factory-Lasered 64-Bit Registration Number Assures Error-Free Device Selection and Absolute
Traceability Because No Two Parts are Alike
Built-in Multidrop Controller for 1-Wire Net
Chip-Based Data Carrier Compactly Stores Information
Data can be Accessed While Affixed to Object
Button Shape is Self-Aligning with Cup-Shaped Probes
Durable Stainless-Steel Case Engraved with Registration Number Withstands Harsh Environments
Easily Affixed with Self-Stick Adhesive Backing, Latched by its Flange, or Locked with a Ring Pressed onto its
Rim
Presence Detector Acknowledges when Reader First Applies Voltage
Meets UL#913 (4th Edit.); Intrinsically Safe Apparatus: Approved Under Entity Concept for use in Class I,
Division 1, Group A, B, C, and D Locations
EXAMPLES OF ACCESSORIES
DS9096P
DS9101
DS9093RA
DS9093A
DS9092
Self-Stick Adhesive Pad
Multipurpose Clip
Mounting Lock Ring
Snap-In Fob
iButton Probe
APPLICATION
The DS1923 is an ideal device to monitor for extended periods of time the temperature and humidity of any object
it is attached to or shipped with, such as fresh produce, medical drugs and supplies and for use in refrigerators and
freezers, as well as for logging climatic data during the transport of sensitive objects and critical processes such as
curing. A 1.27mm diameter hole in the lid of the device allows for air to reach the humidity sensor. The rest of the
electronics inside the DS1923 is sealed so that it is not exposed to ambient humidity. Note that the initial sealing
level of DS1923 achieves IP56. Aging and use conditions can degrade the integrity of the seal over time, so for
applications with significant exposure to liquids, sprays, or other similar environments, it is recommended to place
the Hygrochron under a shield to protect it (See www.maxim-ic.com/AN4126). The hydrophobic filter may not
protect the DS1923 from destruction in the event of full submersion in liquid. Software for setup and data retrieval
through the 1-Wire interface is available for free download from the iButton website (www.ibutton.com). This
software also includes drivers for the serial and USB port of a PC, and routines to access the general-purpose
memory for storing application- or equipment-specific data files.
OVERVIEW
The block diagram in Figure 1 shows the relationships between the major control and memory sections of the
DS1923. The device has six main data components: 1) 64-bit lasered ROM, 2) 256-bit scratchpad, 3) 512-byte
general-purpose SRAM, 4) two 256-bit register pages of timekeeping, control, status, and counter registers and
passwords, 5) 64 bytes of calibration memory, and 6) 8192 bytes of data-logging memory. Except for the ROM and
the scratchpad, all other memory is arranged in a single linear address space. The data logging memory, counter
registers and several other registers are read-only for the user. Both register pages are write-protected while the
device is programmed for a mission. The password registers, one for a read password and another one for a
read/write password can only be written to but never read.
The hierarchical structure of the 1-Wire protocol is shown in Figure 2. The bus master must first provide one of the
eight ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Conditional Search ROM, 5)
Skip ROM, 6) Overdrive-Skip ROM, 7) Overdrive-Match ROM, or 8) Resume. Upon completion of an Overdrive
ROM command byte executed at standard speed, the device enters Overdrive mode, where all subsequent
communication occurs at a higher speed. The protocol required for these ROM function commands is described in
Figure 11. After a ROM function command is successfully executed, the memory and control functions become
accessible and the master can provide any one of the eight available commands. The protocol for these memory
and control function commands is described in Figure 9. All data is read and written least significant bit first.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 1. DS1923 BLOCK DIAGRAM
1-Wire
Port
ROM
Function
Control
IO
64-Bit
Lasered
ROM
Memory
Function
Control
3V Lithium
Parasite
Powered
Circuitry
256-Bit
Scratchpad
General-Purpose
SRAM
(512 Bytes)
DS1923
32.768 kHz
Oscillator
Thermal
Sense
Humidity
Sensor and
ADC2
Internal
Timekeeping &
Control Reg. &
Counters
Register Pages
(64 Bytes)
Calibration Memory
(64 Bytes)
ADC1
Control
Logic
Datalog
Memory
8K Bytes
PARASITE POWER
The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power whenever the IO
input is high. IO provides sufficient power as long as the specified timing and voltage requirements are met. The
advantages of parasite power are two-fold: 1) by parasiting off this input, battery power is conserved, and 2) if the
battery is exhausted for any reason, the ROM may still be read.
64-BIT LASERED ROM
Each DS1923 contains a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code. The next
48 bits are a unique serial number. The last 8 bits are a CRC of the first 56 bits. See Figure 4 for details. The 1Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gates as shown in
Figure 3. The polynomial is X8 + X5 + X4 + 1. Additional information about the Dallas 1-Wire Cyclic Redundancy
Check is available in Dallas Application Note 27.
The shift register bits are initialized to 0. Then starting with the least significant bit of the family code, one bit at a
time is shifted in. After the 8th bit of the family code has been entered, then the serial number followed by the
temperature range code is entered. After the range code has been entered, the shift register contains the CRC
value. Shifting in the 8 bits of CRC returns the shift register to all 0s.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 2. HIERARCHICAL STRUCTURE FOR 1-Wire PROTOCOL
1-Wire net
BUS
Master
Other
Devices
DS1923
Command
Level:
1-Wire ROM Function
Commands
Available
Commands:
Data Field
Affected:
Read ROM
Match ROM
Search ROM
Conditional Search ROM
64-bit ROM, RC-Flag
64-bit ROM, RC-Flag
64-bit ROM, RC-Flag
64-bit ROM, RC-Flag, Alarm Flags,
Search Conditions
RC-Flag
RC-Flag
RC-Flag, OD-Flag
64-bit ROM, RC-Flag, OD-Flag
Skip ROM
Resume
Overdrive Skip
Overdrive Match
Write Scratchpad
Read Scratchpad
Copy Scratchpad w/PW
256-bit Scratchpad, Flags
256-bit Scratchpad
512 byte Data Memory, Registers,
Flags, Passwords
Memory, Registers, Passwords
Read Memory w/PW &
w/CRC
Clear Memory w/PW
DS1923-specific
Memory Function
Commands
Mission Time Stamp, Mission Samples
Counter, Start Delay, Alarm
Flags, Passwords
Memory addresses 020C to 020Fh
Flags, Timestamp, Memory addresses
020C to 020Fh (when logging)
Flags
Forced Conversion
Start Mission w/PW
Stop Mission w/PW
Figure 3. 1-Wire CRC GENERATOR
8
5
4
Polynomial = X + X + X + 1
st
nd
1
STAGE
X
0
rd
2
STAGE
X
1
th
3
STAGE
X
2
th
4
STAGE
X
3
th
5
STAGE
X
4
th
6
STAGE
X
5
th
7
STAGE
X
6
8
STAGE
X
7
INPUT DATA
12 of 53
X
8
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 4. 64-BIT LASERED ROM
MSB
LSB
8-Bit
CRC Code
MSB
LSB
8-Bit Family
Code (41h)
48-Bit Serial Number
MSB
LSB
MSB
LSB
MEMORY
The memory map of the DS1923 is shown in Figure 5. The 512 bytes general-purpose SRAM are located in pages
0 through 15. The various registers to set up and control the device fill page 16 and 17, called Register Pages 1
and 2 (details in Figure 6). Pages 18 and 19 provide storage space for calibration data. The "data log" logging
memory starts at address 1000h (page 128) and extends over 256 pages. The memory pages 20 to 127 are
reserved for future extensions. The scratchpad is an additional page that acts as a buffer when writing to the
SRAM memory or the register page. The data memory can be written at any time. The calibration memory holds
data from the device calibration that can be used to further improve the accuracy of temperature and humidity
readings. See the Software Correction Algorithm sections for details. The last byte of the calibration memory page
stores an 8-bit CRC of the preceding 31 bytes. Page 19 is an exact copy of the data in page 18. While the user can
overwrite the calibration memory, this is not recommended. See the Security by Password section for ways to
protect the memory. The access type for the register pages is register-specific and depends on whether the device
is programmed for a mission. Figure 6 shows the details. The data log memory is read-only for the user. It is written
solely under supervision of the on-chip control logic. Due to the special behavior of the write access logic (write
scratchpad, copy scratchpad) it is recommended to only write full pages at a time. This also applies to the register
pages and the calibration memory. See the Address Register and Transfer Status section for details.
Figure 5. DS1923 MEMORY MAP
32-Byte Intermediate Storage Scratchpad
ADDRESS
0000H to
001FH
0020H to
01FFH
32-Byte General-Purpose SRAM (R/W)
Page 0
General-Purpose SRAM (R/W)
Pages 1
to 15
32-Byte Register Page 1
Page 16
0200H to
021FH
0220H to
023FH
0240H to
025FH
0260H to
027FH
0280H to
0FFFH
32-Byte Register Page 2
Page 17
Calibration Memory Page 1 (R/W)
Page 18
Calibration Memory Page 2 (R/W)
Page 19
(Reserved For Future Extensions)
Pages 20 to 127
1000H to
2FFFH
Data Log Memory (Read-Only)
Pages 128
to 383
13 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 6. DS1923 REGISTER PAGES MAP
ADDR
0200h
0201h
b7
0
0
0202h
0
0203h
0204h
0205h
0206h
0207h
0208h
0209h
020Ah
020Bh
020Ch
020Dh
020Eh
020Fh
0210h
0211h
0212h
0213h
0214h
0215h
0216h
0217h
0218h
0219h
021Ah
0
CENT
021Bh
0
021Ch
021Dh
021Eh
021Fh
0220h
0221h
0222h
0223h
0224h
0225h
0226h
0227h
0228h
⎯
022Fh
0230h
⎯
0237h
0238h
⎯
023Fh
0
CENT
0
0
1
0
1
BOR
1
0
0
b6
b5
10 Seconds
10 Minutes
12/24
20h.
AM/PM
b4
b3
b2
b1
Single Seconds
Single Minutes
10h.
Single Hours
0
10 Date
Single Date
0
0
10m.
Single Months
10 Years
Single Years
Low Byte
0
High Byte
Low Threshold
High Threshold
Low Threshold
High Threshold
Low Byte
0
0
0
0
High Byte
Low Byte
High Byte
0
0
0
0
0
ETHA
1
1
1
1
1
EHHA
0
0
0
0
0
EHSS
1
SUTA
RO
HLFS
TLFS
EHL
1
1
1
HHF
HLF
THF
1
0
WFTA MEMCLR
0
MIP
Low Byte
Center Byte
High Byte
10 Seconds
Single Seconds
10 Minutes
Single Minutes
12/24
20h.
AM/PM
b0
10h.
Single Hours
0
10 Date
Single Date
0
0
10m.
Single Months
10 Years
Single Years
(No Function; Reads 00h)
Low Byte
Center Byte
High Byte
Low Byte
Center Byte
High Byte
Configuration Code
EPW
First Byte
⎯
Eighth Byte
First Byte
⎯
Eighth Byte
(No Function; All of These Bytes Read 00h)
0
ETLA
EHLA
EOSC
ETL
TLF
0
Function
Access*
RealTime
Clock
Registers
R/W; R
Sample
Rate
Temp.
Alarms
Humidity
Alarms
Latest
Temp.
Latest
Humidity
T.Alm.En.
H.Alm.En.
RTC En.
Mis. Cntrl.
Alm. Stat.
Gen. Stat.
Start
Delay
Counter
Mission
Time
Stamp
(N/A)
Mission
Sample
Counter
Device
Sample
Counter
Flavor
PW. Cntrl.
Read
Access
Password
Full
Access
Password
(N/A)
R/W; R
R/W; R
R/W; R
R; R
R; R
R/W; R
R/W; R
R/W; R
R/W; R
R; R
R; R
R/W; R
R; R
R; R
R; R
R; R
R; R
R/W; R
W; ⎯
W; ⎯
R; R
Note: The first entry in column ACCESS TYPE is valid between missions. The second entry shows the applicable
access type while a mission is in progress.
14 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
TIMEKEEPING AND CALENDAR
The real-time clock/alarm and calendar information is accessed by reading/writing the appropriate bytes in the
register page, address 200h to 205h. For readings to be valid, all RTC registers must be read sequentially starting
at address 0200h. Some of the RTC bits are set to 0. These bits always read 0 regardless of how they are written.
The number representation of the real-time clock registers is BCD format (Binary-Coded Decimal).
Real-Time Clock and RTC Alarm Register Bitmap
ADDR
0200h
0201h
0202h
b7
0
0
0
0203h
0204h
0205h
0
CENT
b6
b5
10 Seconds
10 Minutes
b4
12/24
20h.
AM/PM
10h.
b3
b2
b1
Single Seconds
Single Minutes
b0
Single Hours
0
10 Date
0
0
10m.
10 Years
Single Date
Single Months
Single Years
The real-time clock of the DS1923 can run in either 12-hour or 24-hour mode. Bit 6 of the Hours Register (address
202h) is defined as the 12- or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour
mode, bit 5 is the AM/PM bit with logic 1 being PM. In the 24-hour mode, bit 5 is the 20-hour bit (20 to 23 hours).
The CENT bit, bit 7 of the Months Register, can be written by the user. This bit changes its state when the years
counter transitions from 99 to 00.
The calendar logic is designed to automatically compensate for leap years. For every year value that is either 00 or
a multiple of 4 the device will add a 29th of February. This will work correctly up to (but not including) the year
2100.
SAMPLE RATE
The content of the Sample Rate Register (addresses 0206h, 0207h) specifies the time elapse (in seconds if EHSS
= 1, or minutes if EHSS = 0) between two temperature/humidity logging events. The sample rate can be any value
from 1 to 16383, coded as an unsigned 14-bit binary number. If EHSS = 1, the shortest time between logging
events is 1 second and the longest (sample rate = 3FFFh) is 4.55 hours. If EHSS = 0, the shortest is 1 minute and
the longest time is 273.05 hours (sample rate = 3FFFh). The EHSS bit is located in the RTC Control Register at
address 0212h. It is important that the user sets the EHSS bit accordingly while setting the Sample Rate register. A
sample rate of 0000h is not valid and must be avoided under all circumstances. This causes the device to
enter into an unrecoverable state.
Sample Rate Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0206h
Sample Rate Low
0207h
0
0
Sample Rate High
During a mission, there is only read access to these registers. Bits cells marked "0" always read 0 and cannot be
written to 1.
TEMPERATURE CONVERSION
The DS1923 measures temperatures in the range of -20°C to +85°C. Temperature values are represented as a 8or 16-bit unsigned binary number with a resolution of 0.5°C in the 8-bit mode and 0.0625°C in the 16-bit mode.
The higher temperature byte TRH is always valid. In the 16-bit mode only the three highest bits of the lower byte
TRL are valid. The five lower bits all read zero. TRL is undefined if the device is in 8-bit temperature mode. An outof-range temperature reading is indicated as 00h or 0000h when too cold and FFh or FFE0h when too hot.
15 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Latest Temperature Conversion Result Register Bitmap
ADDR
020Ch
020Dh
b7
T2
T10
b6
T1
T9
b5
T0
T8
b4
0
T7
b3
0
T6
b2
0
T5
b1
0
T4
b0
0
T3
TRL
TRH
With TRH and TRL representing the decimal equivalent of a temperature reading the temperature value is
calculated as
ϑ(°C) = TRH/2 - 41 + TRL/512
ϑ(°C) = TRH/2 - 41
(16-bit mode, TLFS = 1, see address 0213h)
(8-bit mode, TLFS = 0, see address 0213h)
This equation is valid for converting temperature readings stored in the data log memory as well as for data read
from the Latest Temperature Conversion Result Register.
To specify the temperature alarm thresholds, the equation above needs to be resolved to
TALM = 2 * ϑ (°C) + 82
Since the temperature alarm threshold is only one byte, the resolution or temperature increment is limited to 0.5°C.
The TALM value needs to be converted into hexadecimal format before it can be written to one of the temperature
alarm threshold registers (Low Alarm address 0208h; High Alarm address 0209h). Independent of the
conversion mode (8- or 16-bit) only the most significant byte of a temperature conversion is used to determine
whether an alarm is generated.
Temperature Conversion Examples
Mode
8-bit
8-bit
16-bit
16-bit
hex
54h
17h
54h
17h
TRH
decimal
84
23
84
23
hex
⎯
⎯
00h
60h
TRL
decimal
⎯
⎯
0
96
ϑ(°C)
1.0
-29.5
1.000
-29.3125
Temperature Alarm Threshold Examples
ϑ(°C)
25.5
-10.0
TALM
hex
decimal
133
85h
62
3Eh
HUMIDITY CONVERSION
In addition to temperature, the DS1923 can log humidity data in 8-bit or 16-bit format. Humidity values are
represented as 8- or 16-bit unsigned binary numbers with a resolution of 0.64%RH in the 8-bit mode and 0.04
%RH in the 16-bit mode.
The DS1923 reads data from its humidity sensor whenever a Forced Conversion command is executed (see
Memory/Control Function Commands) or during a mission, if the device is set up to log humidity data. Regardless
of its setup, the DS1923 always reads 16 bits from the humidity sensor. The result of the latest humidity reading
is found at address 020Eh (low byte) and 020Fh (high byte). The most significant bit read from the humidity
sensor will always be found as H11 at address 020Fh. Due to the 12-bit digital output of the humidity sensor, the
lower 4 bits in 16-bit format are undefined.
16 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Latest Humidity Conversion Result Register Bitmap
ADDR
020Eh
020Fh
b7
H3
H11
b6
H2
H10
b5
H1
H9
b4
H0
H8
b3
X
H7
b2
X
H6
b1
X
H5
b0
X
H4
HRL
HRH
During a mission, if humidity logging is enabled, the HRH byte (H11 to H4) is always recorded. The HRL byte is
only recorded if the DS1923 is set up for 16-bit humidity logging. The logging mode (8-bit or 16-bit) is selected
through the HLFS bit at the Mission Control Register, address 0213h.
With HRH and HRL representing the decimal equivalent of a humidity reading the actual humidity is calculated
according to the algorithms shown in the table below.
16-Bit Mode, HLFS = 1
8-Bit Mode, HLFS = 0
IVAL = (HRH * 256 + HRL)/16
(N/A)
Round IVAL down to the nearest integer; this eliminates the undefined 4 bits of HRL.
ADVAL = IVAL*5.02/4096
ADVAL = HRH*5.02/256
HUMIDITY(%RH) = (ADVAL - 0.958)/0.0307
The result is a raw humidity reading that needs to be corrected to achieve the specified accuracy. See the Software
Correction Algorithm for Humidity section for further details.
To specify the humidity alarm thresholds, the equation needs to be resolved to:
ADVAL = HUMIDITY(%RH) * 0.0307 + 0.958
HALM = ADVAL * 256/5.02
Round HALM to the nearest integer.
The HALM value needs to be converted into hexadecimal before it can be written to one of the humidity alarm
threshold registers (Low Alarm address 020Ah; High Alarm address 020B). Independent of the conversion
mode (8-or 16-bit) only the most significant byte of a humidity conversion is used to determine whether an alarm
will be generated. The alarm thresholds are applied to the raw humidity readings. Therefore, if software correction
is used, the effect of the software correction is to be reversed before calculating a humidity alarm threshold.
Example: let the desired alarm threshold be 60%RH. The 60% threshold may correspond to a raw reading of
65%RH (i.e., before correction). To set a 60%RH (after correction) threshold, the HALM value then needs to be
calculated for 65%RH.
Humidity Conversion Examples
Mode
hex
B5h
67h
B5h
67h
8-bit
8-bit
16-bit
16-bit
HRH
decimal
181
103
181
103
hex
⎯
⎯
C0h
30h
HRL
decimal
⎯
⎯
12
48
Humidity(%RH)
84.41
34.59
84.89
34.70
Humidity Alarm Threshold Examples
Humidity(%RH)
65
25
HALM
hex
decimal
151
97h
88
58h
These examples do not include the effects of software correction.
17 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
TEMPERATURE SENSOR ALARM
The DS1923 has two Temperature Alarm Threshold registers (address 0208h, 0209h) to store values, which
determine whether a critical temperature has been reached. A temperature alarm is generated if the device
measures an alarming temperature AND the alarm signaling is enabled. The bits ETLA and ETHA that enable the
temperature alarm are located in the Temperature Sensor Control Register. The temperature alarm flags TLF and
THF are found in the Alarm Status Register at address 0214h.
Temperature Sensor Control Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0210h
0
0
0
0
0
0
ETHA
ETLA
During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 0 and
cannot be written to 1.
Register Details
Bit Description
Bit(s)
ETLA: Enable Temperature Low Alarm
b0
ETHA: Enable
Temperature High Alarm
b1
Definition
This bit controls whether, during a mission, the Temperature Low Alarm
Flag TLF can be set, if a temperature conversion results in a value equal
to or lower than the value in the Temperature Low Alarm Threshold
Register. If ETLA is 1, temperature low alarms are enabled. If ETLA is 0,
temperature low alarms are not generated.
This bit controls whether, during a mission, the Temperature High Alarm
Flag THF can be set, if a temperature conversion results in a value
equal to or higher than the value in the Temperature High Alarm
Threshold Register. If ETHA is 1, temperature high alarms are enabled.
If ETHA is 0, temperature high alarms are not generated.
HUMIDITY ALARM
The DS1923 has two Humidity Alarm Threshold registers (address 020Ah, 020Bh) to store values, which
determine whether humidity readings can generate an alarm. Such an alarm is generated if the humidity data read
from the sensor qualifies for an alarm AND the alarm signaling is enabled. The bits EHLA and EHHA that enable
the humidity alarm are located in the Humidity Sensor Control Register. The corresponding alarm flags HLF and
HHF are found in the Alarm Status Register at address 0214h.
Humidity Sensor Control Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0211h
1
1
1
1
1
1
EHHA
EHLA
During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 1 and
cannot be written to 0.
Register Details
Bit Description
Bit(s)
EHLA: Enable Humidity
Low Alarm
b0
EHHA: Enable Humidity
High Alarm
b1
Definition
This bit controls whether, during a mission, the Humidity Low Alarm Flag
HLF can be set, if a value from the humidity sensor is equal to or lower
than the value in the Humidity Low Alarm Threshold Register. If EHLA is
1, humidity low alarms are enabled. If EHLA is 0, humidity low alarms
are not generated.
This bit controls whether, during a mission, the Humidity High Alarm
Flag HHF can be set, if a value from the humidity sensor is equal to or
higher than the value in the Humidity High Alarm Threshold Register. If
EHHA is 1, humidity high alarms are enabled. If EHHA is 0, humidity
high alarms are not generated.
18 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
REAL-TIME CLOCK CONTROL
To minimize the power consumption of a DS1923, the real-time clock oscillator should be turned off when device is
not in use. The oscillator on/off bit is located in the RTC control register. This register also includes the EHSS bit,
which determines whether the sample rate is specified in seconds or minutes.
RTC Control Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0212h
0
0
0
0
0
0
EHSS EOSC
During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 0 and
cannot be written to 1.
Register Details
Bit Description
Bit(s)
EOSC: Enable Oscillator
b0
EHSS: Enable High Speed
Sample
b1
Definition
This bit controls the crystal oscillator of the real-time clock. When set to
logic 1, the oscillator starts operation. When written to logic 0, the
oscillator stops and the device is in a low-power data retention mode.
This bit must be 1 for normal operation. A temperature or humidity
conversion must not be attempted while the RTC oscillator is
stopped. This causes the device to enter into an unrecoverable state.
This bit controls the speed of the Sample Rate counter. When set to
logic 0, the sample rate is specified in minutes. When set to logic 1, the
sample rate is specified in seconds.
MISSION CONTROL
The DS1923 is set up for its operation by writing appropriate data to its special function registers, which are located
in the two register pages. The settings in the Mission Control Register determine whether temperature and/or
humidity is logged, which format (8 or 16 bits) is to be used and whether old data can be overwritten by new data,
once the data log memory is full. An additional control bit can be set to tell the DS1923 to wait with logging data
until a temperature alarm is encountered.
Mission Control Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0213h
1
1
SUTA
RO
HLFS
TLFS
EHL
ETL
During a mission, there is only read access to this register. Bits 6 and 7 have no function. They always read 1 and
cannot be written to 0.
Register Details
Bit Description
Bit(s)
ETL: Enable Temperature
Logging
b0
EHL: Enable Humidity
Logging
b1
TLFS: Temperature
Logging Format Selection
b2
Definition
To set up the device for a temperature-logging mission, this bit must be
set to logic 1. To successfully start a mission, ETL or EHL must be 1. If
temperature logging is enabled, the recorded temperature values are
always stored starting at address 1000h.
To set up the DS1923 for a humidity-logging mission, this bit must be
set to logic 1. If temperature and humidity logging are enabled, the
recorded humidity values will begin at address 2000h (TLFS = HLFS) or
1A00h (TLFS = 0; HLFS = 1) or 2400h (TLFS = 1; HLFS = 0). If only
humidity logging is enabled, the recorded values are stored starting at
address 1000h. Since humidity data has little scientific value without
knowing the temperature, typically both, humidity and temperature
logging are enabled, i. e., ETL and EHL are set to 1.
This bit specifies the format used to store temperature readings in the
data log memory. If this bit is 0, the data will be stored in 8-bit format. If
this bit is 1, the 16-bit format will be used (higher resolution). With 16-bit
format, the most-significant byte is stored at the lower address.
19 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Bit(s)
Definition
This bit specifies the format used to store humidity readings in the data
log memory. If this bit is 0, the data will be stored in 8-bit format. If this
HLFS: Humidity Logging
b3
Format Selection
bit is 1, the 16-bit format is used (higher resolution). With 16-bit format,
the most-significant byte is stored at the lower address.
This bit controls whether, during a mission, the data log memory is
overwritten with new data or whether data logging is stopped once the
data log memory is full. Setting this bit to 1 enables the rollover and data
RO: Rollover Control
b4
logging continues at the beginning, overwriting previously collected data.
If this bit is 0, the logging and conversions will stop once the data log
memory is full. However, the RTC will continue to run and the MIP bit
will remain set until the Stop Mission command is performed.
This bit specifies whether a mission begins immediately (includes
delayed start) or if a temperature alarm will be required to start the
mission. If this bit is 1, the device will perform a temperature conversion
at the selected sample rate and begin with data logging only if an
SUTA: Start Mission upon
b5
alarming temperature (high alarm or low alarm) was found. The first
Temperature Alarm
logged temperature will be when the alarm occurred. However, the
Mission Sample Counter will not increment. The Start Upon Temperature Alarm function is only available if temperature logging is enabled
(ETL = 1).
Bit Description
ALARM STATUS
The fastest way to determine whether a programmed temperature or humidity threshold was exceeded during a
mission is through reading the Alarm Status Register. In a networked environment that contains multiple DS1923
iButtons the devices that encountered an alarm can quickly be identified by means of the Conditional Search
command (see ROM Function Commands). The humidity and temperature alarm only occurs if enabled (see
Temperature Sensor Alarm and Humidity Alarm). The BOR alarm is always enabled.
Alarm Status Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0214h
BOR
1
1
1
HHF
HLF
THF
TLF
There is only read access to this register. Bits 4 to 6 have no function. They always read 1. All five alarm status bits
are cleared simultaneously when the Clear Memory function is invoked. See Memory and Control Functions for
details.
Register Details
Bit Description
Bit(s)
TLF: Temperature Low
Alarm Flag
b0
THF: Temperature High
Alarm Flag
b1
HLF: Humidity Low Alarm
Flag
b2
HHF: Humidity High Alarm
Flag
b3
BOR: Battery On Reset
Alarm
b7
Definition
If this bit reads 1, there was at least one temperature conversion during
a mission revealing a temperature equal to or lower than the value in the
Temperature Low Alarm Register. A forced conversion can affect the
TLF bit. This bit can also be set with the initial alarm in the SUTA = 1
mode.
If this bit reads 1, there was at least one temperature conversion during
a mission revealing a temperature equal to or higher than the value in
the Temperature High Alarm Register. A forced conversion can affect
the THF bit. This bit can also be set with the initial alarm in the SUTA =
1 mode.
If this bit reads 1, there was at least one humidity reading during a
mission revealing a value equal to or lower than the value in the Humidity Low Alarm Register. A forced conversion can affect the HLF bit.
If this bit reads 1, there was at least one humidity reading during a
mission revealing a value equal to or higher than the value in the Humidity High Alarm Register. A forced conversion can affect the HHF bit.
If this bit reads 1, the device has performed a power-on reset. This
indicates that the device has experienced a shock big enough to
interrupt the internal battery power supply. The device can still appear
functional, but it has lost its factory calibration. Any data found in the
data log memory should be disregarded.
20 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
GENERAL STATUS
The information in the general status register tells the host computer whether a mission-related command was
executed successfully. Individual status bits indicate whether the DS1923 is performing a mission, waiting for a
temperature alarm to trigger the logging of data or whether the data from the latest mission has been cleared.
General Status Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
0215h
1
1
0
WFTA MEMCLR
0
MIP
There is only read access to this register. Bits 0, 2, 5, 6, and 7 have no function.
b0
0
Register Details
Bit Description
Bit(s)
MIP: Mission In Progress
b1
MEMCLR: Memory
Cleared
b3
WFTA: Waiting for
Temperature Alarm
b4
Definition
If this bit reads 1 the device has been set up for a mission and this
mission is still in progress. The MIP bit returns from logic 1 to logic 0
when a mission is ended. See function commands Start Mission and
Stop Mission.
If this bit reads 1, the Mission Time Stamp, Mission Sample Counter, as
well as all the alarm flags of the Alarm Status Register have been
cleared in preparation of a new mission. Executing the Clear Memory
command clears these memory sections. The MEMCLR bit returns to 0
as soon as a new mission is started by using the Start Mission
command. The memory has to be cleared in order for a mission to start.
If this bit reads 1, the Mission Start upon Temperature Alarm was
selected and the Start Mission command was successfully executed, but
the device has not yet experienced the temperature alarm. This bit is
cleared after a temperature alarm event, but is not affected by the Clear
Memory command. Once set, WFTA remains set if a mission is stopped
before a temperature alarm occurs. To clear WFTA manually before
starting a new mission, set the high temperature alarm (address 0209h)
to -40°C and perform a forced conversion.
MISSION START DELAY
The content of the Mission Start Delay Counter tells how many minutes have to expire from the time a mission was
started until the first measurement of the mission will take place (SUTA = 0) or until the device will start testing the
temperature for a temperature alarm (SUTA = 1). The Mission Start Delay is stored as an unsigned 24-bit integer
number. The maximum delay is 16777215 minutes, equivalent to 11650 days or roughly 31 years. If the start delay
is non-zero and the SUTA bit is set to 1, first the delay has to expire before the device starts testing for temperature
alarms to begin logging data.
Mission Start Delay Counter
ADDR
b7
b6
b5
b4
b3
b2
0216h
Delay Low Byte
0217h
Delay Center Byte
0218h
Delay High Byte
During a mission, there is only read access to these registers.
b1
b0
For a typical mission, the Mission Start Delay is 0. If a mission is too long for a single DS1923 to store all readings
at the selected sample rate, one can use several devices and set the Mission Start Delay for the second device to
start recording as soon as the memory of the first device is full, and so on. The RO bit in the Mission Control
Register (address 0213h) must be set to 0 to prevent overwriting of collected data once the data log memory is full.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
MISSION TIME STAMP
The Mission Time Stamp indicates the date and time of the first temperature and/or humidity sample of the
mission. There is only read access to the Mission Time Stamp Register.
Mission Time Stamp Registers Bitmap
ADDR
0219h
021Ah
021Bh
b7
0
0
0
b6
b5
10 Seconds
10 Minutes
b4
12/24
20h.
AM/PM
10h.
021Ch
0
0
021Dh
021Eh
CENT
b3
b2
b1
Single Seconds
Single Minutes
Single Hours
10 Date
0
0
10 Years
b0
Single Date
10m.
Single Months
Single Years
MISSION PROGRESS INDICATOR
Depending on settings in the Mission Control Register (address 0213h) the DS1923 logs temperature and/or
humidity in 8-bit or 16-bit format. The description of the ETL and EHL bit explains where the device stores data in
its data log memory. The Mission Sample Counter together with the starting address and the logging format (8 or
16 bits) provides the information to identify valid blocks of data that have been gathered during the current (MIP =
1) or latest mission (MIP = 0). See section Data log Memory Usage for an illustration. Note that when SUTA = 1,
the Mission Sample Counter does not increment when the first sample is logged.
Mission Sample Counter Register Map
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0220h
Low Byte
0221h
Center Byte
0222h
High Byte
There is only read access to this register. Note that when both the internal temperature and humidity logging are
enabled, the two log readings are counted as one event in the Mission Sample Counter and Device Sample
Counter.
The number read from the Mission Sample Counter indicates how often the DS1923 woke up during a mission to
measure temperature and/or humidity. The number format is 24-bit unsigned integer. The Mission Sample Counter
is reset through the Clear Memory command.
OTHER INDICATORS
The Device Sample Counter is similar to the Mission Sample Counter. During a mission this counter increments
whenever the DS1923 wakes up to measure and log data and when the device is testing for a temperature alarm in
SUTA mode. Between missions the counter increments whenever the Forced Conversion command is executed.
This way the Device Sample Counter functions like a gas gauge for the battery that powers the iButton.
Device Sample Counter Register Map
ADDR
b7
b6
b5
0223h
0224h
0225h
There is only read access to this register.
b4
b3
Low Byte
Center Byte
High Byte
b2
b1
b0
The Device Sample Counter is reset to zero when the iButton is assembled. The counter increments a couple of
times during final test. The number format is 24-bit unsigned integer. The maximum number that can be
represented in this format is 16777215.
The Device Configuration Byte is used to allow the master to distinguish between the DS2422 chip, and the
DS1923, DS1922L, and DS1922T iButtons. The table below shows the codes assigned to the various devices.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Device Configuration Byte
ADDR
b7
b6
b5
b4
b3
0226h
0
0
0
0
0
0226h
0
0
1
0
0
0226h
0
1
0
0
0
0226h
0
1
1
0
0
There is only read access to this register.
b2
0
0
0
0
b1
0
0
0
0
b0
0
0
0
0
DS2422
DS1923
DS1922L
DS1922T
SECURITY BY PASSWORD
The DS1923 is designed to use two passwords that control read access and full access. Reading from or writing to
the scratchpad as well as the forced conversion command does not require a password. The password needs to
be transmitted right after the command code of the memory or control function. If password checking is enabled the
password transmitted is compared to the passwords stored in the device. The data pattern stored in the Password
Control register determines whether password checking is enabled.
Password Control Register
ADDR
b7
b6
b5
b4
b3
0227h
EPW
During a mission, there is only read access to this register.
b2
b1
b0
To enable password checking, the EPW bits need to form a binary pattern of 10101010 (AAh). The default pattern
of EPW is different from AAh. If the EPW pattern is different from AAh, any pattern will be accepted, as long as it
has a length of exactly 64 bits. Once enabled, changing the passwords and disabling password checking requires
the knowledge of the current full-access password.
Before enabling password checking, passwords for read-only access as well as for full access (read/write/control)
need to be written to the password registers. Setting up a password or enabling/disabling the password checking is
done in the same way as writing data to a memory location, only the address is different. Since they are located in
the same memory page, both passwords can be redefined at the same time.
Read Access Password Register
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0228h
RP7
RP6
RP5
RP4
RP3
RP2
RP1
RP0
0229h
RP15
RP14
RP13
RP12
RP11
RP10
RP9
RP8
⎯
⎯
⎯
022Eh
RP55
RP54
RP53
RP52
RP51
RP50
RP49
RP48
022Fh
RP63
RP62
RP61
RP60
RP59
RP58
RP57
RP56
There is only write access to this register. Attempting to read the password will report all zeros. The password
cannot be changed while a mission is in progress.
The Read Access Password needs to be transmitted exactly in the sequence RP0, RP1… RP62, RP63. This
password only applies to the function “Read Memory with CRC”. The DS1923 delivers the requested data only if
the password transmitted by the master was correct or if password checking is not enabled.
Full-Access Password Register
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0230h
FP7
FP6
FP5
FP4
FP3
FP2
FP1
FP0
0231h
FP15
FP14
FP13
FP12
FP11
FP10
FP9
FP8
⎯
⎯
⎯
0236h
FP55
FP54
FP53
FP52
FP51
FP50
FP49
FP48
0237h
FP63
FP62
FP61
FP60
FP59
FP58
FP57
FP56
There is only write access to this register. Attempting to read the password will report all zeros. The password
cannot be changed while a mission is in progress.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
The Full Access Password needs to be transmitted exactly in the sequence FP0, FP1… FP62, FP63. It affects the
functions “Read Memory with CRC”, “Copy Scratchpad”, “Clear Memory”, “Start Mission”, and “Stop Mission”. The
DS1923 executes the command only if the password transmitted by the master was correct or if password
checking is not enabled
Due to the special behavior of the write access logic, the Password Control Register and both passwords must be
written at the same time. When setting up new passwords, always verify (read back) the scratchpad before sending
the copy scratchpad command. After a new password is successfully copied from the scratchpad to its memory
location, erase the scratchpad by filling it with new data (write scratchpad command). Otherwise a copy of the
passwords will remain in the scratchpad for public read access.
DATA LOG MEMORY USAGE
Once setup for a mission, the DS1923 logs the temperature measurements and/or humidity at equidistant time
points entry after entry in its data log memory. The data log memory is able to store 8192 entries in 8-bit format or
4096 entries in 16-bit format (Figure 7A). If temperature as well as humidity is logged, both in the same format, the
memory is split into two equal sections that can store 4096 8-bit entries or 2048 16-bit entries (Figure 7B). If the
device is set up to log data in different formats, e. g., temperature in 8-bit and humidity in 16-bit format, the memory
is split into blocks of different size, accommodating 2560 entries for either data source (Figure 7C). In this case, the
upper 256 bytes are not used. In 16-bit format, the higher 8 bits of an entry are stored at the lower address.
Knowing the starting time point (Mission Time Stamp) and the interval between temperature measurements one
can reconstruct the time and date of each measurement.
There are two alternatives to the way the DS1923 behaves after the data log memory is filled with data. The user
can program the device to either stop any further recording (disable “rollover”) or overwrite the previously recorded
data (enable “rollover”), one entry at a time, starting again at the beginning of the respective memory section. The
contents of the Mission Sample Counter in conjunction with the sample rate and the Mission Time Stamp then
allows reconstructing the time points of all values stored in the data log memory. This gives the exact history over
time for the most recent measurements taken. Earlier measurements cannot be reconstructed.
Figure 7A. ONE CHANNEL LOGGING
ETL = 1; EHL = 0 or
ETL = 0; EHL = 1
TLFS = HLFS = 0
ETL = 1; EHL = 0 or
ETL = 0; EHL = 1
TLFS = HLFS = 1
1000h
8192
8-bit entries
Temperature
or
Humidity data
1000h
With 16-bit format,
the most-significant
byte is stored at the
lower address.
4096
16-bit entries
Temperature
or
Humidity data
2FFFh
2FFFh
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 7B. TWO CHANNEL LOGGING, EQUAL RESOLUTION
ETL = EHL = 1
TLFS = HLFS = 0
ETL = EHL = 1
TLFS = HLFS = 1
1000h
Temperature
4096
8-bit entries
1000h
Temperature
2048
16-bit entries
1FFFh
2000h
Humidity Data
4096
8-bit entries
1FFFh
2000h
With 16-bit format,
the most-significant
byte is stored at the
lower address.
Humidity Data
2048
16-bit entries
2FFFh
2FFFh
Figure 7C. TWO CHANNEL LOGGING, DIFFERENT RESOLUTION
ETL = EHL = 1
TLFS = 0; HLFS = 1
Temperature
2560
8-bit entries
1000h
19FFh
1A00h
Humidity Data
2560
16-bit entries
1000h
Temperature
2560
16-bit entries
23FFh
2DFFh
(not used)
ETL = EHL = 1
TLFS = 1; HLFS = 0
2E00h
2FFFh
Humidity Data
2560
8-bit entries
2400h
(not used)
2E00h
2FFFh
With 16-bit format,
the most-significant
byte is stored at the
lower address.
2DFFh
MISSIONING
The typical task of the DS1923 iButton is recording temperature and/or humidity. Before the device can perform
this function, it needs to be set up properly. This procedure is called missioning.
First of all, DS1923 needs to have its real-time clock set to valid time and date. This reference time may be the
local time, or, when used inside of a mobile unit, UTC (also called GMT, Greenwich Mean Time) or any other time
standard that was agreed upon. The real-time clock oscillator must be running (EOSC = 1). The memory assigned
to store the Mission Time Stamp, Mission Sample Counter, and Alarm Flags must be cleared using the Memory
Clear command. To enable the device for a mission, at least one of the enable logging bits (ETL, EHL) must be set
to 1. These are general settings that have to be made in any case, regardless of the type of object to be monitored
and the duration of the mission.
If alarm signaling is desired, the temperature alarm and/or humidity alarm low and high thresholds must be defined.
How to convert a temperature value into the binary code to be written to the threshold registers is described under
“Temperature Conversion” earlier in this document. Determining the thresholds for the humidity alarm is described
in section “Humidity Conversion”. In addition, the temperature and/or humidity alarm must be enabled for the low25 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
and/or high-threshold. This will make the device respond to a Conditional Search command (see ROM Function
Commands), provided that an alarming condition has been encountered.
The setting of the RO bit (rollover enable) and sample rate depends on the duration of the mission and the
monitoring requirements. If the most recently logged data is important, the rollover should be enabled (RO = 1).
Otherwise one should estimate the duration of the mission in minutes and divide the number by 8192 (single
channel 8-bit format) or 4096 (single channel 16-bit format, two channels 8-bit format) or 2048 (two channels 16-bit
format) or 2560 (two channels, one 8-bit and one 16-bit format) to calculate the value of the sample rate (number of
minutes between conversions). If the estimated duration of a mission is 10 days (= 14400 minutes), for example,
then the 8192-byte capacity of the data log memory would be sufficient to store a new 8-bit value every 1.8 minutes
(110 seconds). If the data log memory of the DS1923 is not large enough to store all readings, one can use several
devices and set the Mission Start Delay to values that make the second device start logging as soon as the
memory of the first device is full, and so on. The RO-bit needs to be set to 0 to disable rollover that would
otherwise overwrite the logged data.
After the RO bit and the Mission Start Delay are set, the sample rate needs to be written to the Sample Rate
Register. The sample rate may be any value from 1 to 16383, coded as an unsigned 14-bit binary number. A
sample rate of all zeros is not valid and must be avoided under all circumstances. This causes the device to
enter into an unrecoverable state. The fastest sample rate is one sample per second (EHSS = 1, Sample Rate =
0001h) and the slowest is one sample every 273.05 hours (EHSS = 0, Sample Rate = 3FFFh). To get one sample
every 6 minutes, for example, the sample rate value needs to be set to 6 (EHSS = 0) or 360 decimal (equivalent to
0168h at EHSS = 1).
If there is a risk of unauthorized access to the DS1923 or manipulation of data, one should define passwords for
read access and full access. Before the passwords become effective, their use needs to be enabled. See Security
by Password for more details.
The last step to begin a mission is to issue the Start Mission command. As soon as it has received this command,
the DS1923 sets the MIP flag and clear the MEMCLR flag. With the immediate/delayed start mode (SUTA = 0),
after as many minutes as specified by the Mission Start Delay are over, the device wakes up, copies the current
date and time to the mission time stamp register, and logs the first entry of the mission. This increments both the
Mission Sample Counter and Device Sample Counter. All subsequent log entries are made as specified by the
value in the Sample Rate Register and the EHSS bit.
If the Start Upon Temperature Alarm mode is chosen (SUTA = 1) and temperature logging is enabled (ETL = 1) the
DS1923 first waist until the start delay is over. Then the device wakes up in intervals as specified by the sample
rate and EHSS bit and measure the temperature. This increments the Device Sample Counter only. The first
sample of the mission is logged when the temperature alarm occurred. However, the Mission Sample Counter will
not increment. One sample period later the Mission Time Stamp is set. From then on, both the Mission Sample
Counter and Device Sample Counter increment at the same time. All subsequent log entries will be made as
specified by the value in the Sample Rate Register and the EHSS bit.
The general-purpose memory operates independently of the other memory sections and is not write-protected
during a mission. All memory of the DS1923 can be read at any time, e. g., to watch the progress of a mission.
Attempts to read the passwords will read 00h bytes instead of the data that is stored in the password registers.
ADDRESS REGISTERS AND TRANSFER STATUS
Because of the serial data transfer, the DS1923 employs three address registers, called TA1, TA2, and E/S (Figure
8). Registers TA1 and TA2 must be loaded with the target address to which the data will be written or from which
data will be sent to the master upon a Read command. Register E/S acts like a byte counter and transfer status
register. It is used to verify data integrity with Write commands. Therefore, the master only has read access to this
register. The lower 5 bits of the E/S Register indicate the address of the last byte that has been written to the
scratchpad. This address is called Ending Offset. The DS1923 requires that the Ending Offset is always 1Fh for
a Copy Scratchpad to function. Bit 5 of the E/S Register, called PF or “partial byte flag,” is set if the number of
data bits sent by the master is not an integer multiple of 8. Bit 6 is always a 0. Note that the lowest 5 bits of the
target address also determine the address within the scratchpad, where intermediate storage of data begins. This
address is called byte offset. If the target address for a Write command is 13Ch, for example, then the scratchpad
stores incoming data beginning at the byte offset 1Ch and is full after only 4 bytes. The corresponding ending offset
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
in this example is 1Fh. For best economy of speed and efficiency, the target address for writing should point to the
beginning of a page, i.e., the byte offset is 0. Thus the full 32-byte capacity of the scratchpad is available, resulting
also in the ending offset of 1Fh. The ending offset together with the Partial and Overflow Flag is mainly a means to
support the master checking the data integrity after a Write command. The highest valued bit of the E/S Register,
called AA or Authorization Accepted, indicates that a valid copy command for the scratchpad has been received
and executed. Writing data to the scratchpad clears this flag.
Figure 8. ADDRESS REGISTERS
Bit #
7
6
5
4
3
2
1
0
Target Address (TA1)
T7
T6
T5
T4
T3
T2
T1
T0
Target Address (TA2)
T15
T14
T13
T12
T11
T10
T9
T8
Ending Address with
Data Status (E/S)
(Read Only)
AA
0
PF
E4
E3
E2
E1
E0
WRITING WITH VERIFICATION
To write data to the DS1923, the scratchpad has to be used as intermediate storage. First the master issues the
Write Scratchpad command to specify the desired target address, followed by the data to be written to the
scratchpad. In the next step, the master sends the Read Scratchpad command to read the scratchpad and to verify
data integrity. As preamble to the scratchpad data, the DS1923 sends the requested target address TA1 and TA2
and the contents of the E/S Register. If the PF flag is set, data did not arrive correctly in the scratchpad. The
master does not need to continue reading; it can start a new trial to write data to the scratchpad. Similarly, a set AA
flag indicates that the Write command was not recognized by the device. If everything went correctly, both flags are
cleared and the ending offset indicates the address of the last byte written to the scratchpad. Now the master can
continue verifying every data bit. After the master has verified the data, it has to send the Copy Scratchpad
command. This command must be followed exactly by the data of the three address registers TA1, TA2, and E/S
as the master has read them verifying the scratchpad. As soon as the DS1923 has received these bytes, it copies
the data to the requested location beginning at the target address.
MEMORY- AND CONTROL-FUNCTION COMMANDS
The “Memory/Control Function Flow Chart” (Figure 9) describes the protocols necessary for accessing the memory
and the special function registers of the DS1923. An example on how to use these and other functions to set up the
DS1923 for a mission is included at the end of this document, preceding the Electrical Characteristics section. The
communication between master and DS1923 takes place either at regular speed (default, OD = 0) or at Overdrive
Speed (OD = 1). If not explicitly set into the Overdrive Mode the DS1923 assumes regular speed. Internal memory
access during a mission has priority over external access through the 1-Wire interface. This affects several of the
commands described below. See Memory Access Conflicts for details and remedies.
Write Scratchpad Command [0Fh]
After issuing the Write Scratchpad command, the master must first provide the 2-byte target address, followed by
the data to be written to the scratchpad. The data will be written to the scratchpad starting at the byte offset
(T4:T0). The master has to send as many bytes as are needed to reach the Ending Offset of 1Fh. If a data byte is
incomplete, its content is ignored and the partial byte flag PF is set.
When executing the Write Scratchpad command the CRC generator inside the DS1923 (see Figure 15) calculates
a CRC of the entire data stream, starting at the command code and ending at the last data byte sent by the master.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
This CRC is generated using the CRC16 polynomial by first clearing the CRC generator and then shifting in the
command code (0Fh) of the Write Scratchpad command, the Target Addresses TA1 and TA2 as supplied by the
master and all the data bytes. If the ending offset is 11111b, the master may send 16 read time slots and will
receive the inverted CRC16 generated by the DS1923.
Note that both register pages are write-protected during a mission. Although the Write Scratchpad command will
work normally at any time, the subsequent copy scratchpad to a register page will fail during a mission.
Read Scratchpad Command [AAh]
This command is used to verify scratchpad data and target address. After issuing the Read Scratchpad command,
the master begins reading. The first 2 bytes will be the target address. The next byte will be the ending offset/data
status byte (E/S) followed by the scratchpad data beginning at the byte offset (T4:T0), as shown in Figure 8. The
master may continue reading data until the end of the scratchpad after which it will receive an inverted CRC16 of
the command code, Target Addresses TA1 and TA2, the E/S byte, and the scratchpad data starting at the target
address. After the CRC is read, the bus master will read logical 1s from the DS1923 until a reset pulse is issued.
Copy Scratchpad with Password [99h]
This command is used to copy data from the scratchpad to the writable memory sections. After issuing the Copy
Scratchpad command, the master must provide a 3-byte authorization pattern, which can be obtained by reading
the scratchpad for verification. This pattern must exactly match the data contained in the three address registers
(TA1, TA2, E/S, in that order). Next the master must transmit the 64-bit full-access password. If passwords are
enabled and the transmitted password is different from the stored full-access password, the Copy Scratchpad with
Password command will fail. Then the device stops communicating and waits for a reset pulse. If the password
was correct or if passwords were not enabled, the device tests the 3-byte authorization code. If the authorization
code pattern matches, the AA (Authorization Accepted) flag is set and the copy begins. A pattern of alternating 1s
and 0s are transmitted after the data has been copied until the master issues a reset pulse. While the copy is in
progress any attempt to reset the part is ignored. Copy typically takes 2µs per byte.
The data to be copied is determined by the three address registers. The scratchpad data from the beginning offset
through the ending offset will be copied, starting at the target address. The AA flag remains at logic 1 until it is
cleared by the next Write Scratchpad command. With suitable password, the copy scratchpad always functions for
the 16 pages of data memory and the 2 pages of calibration memory. While a mission is in progress, write attempts
to the register pages will not be successful. The AA bit (Authorization Accepted) remaining at 0 will indicate this.
Read Memory with Password and CRC [69h]
The Read Memory with CRC command is the general function to read from the device. This command generates
and transmits a 16-bit CRC following the last data byte of a memory page.
After having sent the command code of the Read Memory with CRC command, the bus master sends a 2-byte
address that indicates a starting byte location. Next the master must transmit one of the 64-bit passwords. If
passwords are enabled and the transmitted password does not match one of the stored passwords, the Read
Memory with Password and CRC command fails. The device will stop communicating and will wait for a reset
pulse. If the password was correct or if passwords were not enabled, the master reads data from the DS1923
beginning from the starting address and continuing until the end of a 32-byte page is reached. At that point the bus
master sends 16 additional read data time slots and receive the inverted 16-bit CRC. With subsequent read-data
time slots the master will receive data starting at the beginning of the next memory page followed again by the
CRC for that page. This sequence continues until the bus master resets the device. When trying to read the
passwords or memory areas that are marked as "reserved", the DS1923 transmits 00h or FFh bytes, respectively.
The CRC at the end of a 32-byte memory page is based on the data as it was transmitted.
With the initial pass through the Read Memory with CRC flow, the 16-bit CRC value is the result of shifting the
command byte into the cleared CRC generator followed by the 2 address bytes and the contents of the data
memory. Subsequent passes through the Read Memory with CRC flow will generate a 16-bit CRC that is the result
of clearing the CRC generator and then shifting in the contents of the data memory page. After the 16-bit CRC of
the last page is read, the bus master receives logical 1s from the DS1923 until a reset pulse is issued. The Read
Memory with CRC command sequence can be ended at any point by issuing a reset pulse.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 9-1. MEMORY/CONTROL FUNCTION FLOW CHART
From ROM Functions
Flow Chart (Figure 11)
Master TX Memory or
Control Fkt. Command
0FH
Write
Scratchpad
AAH
Read
Scratchpad
N
Y
Y
Master TX
TA1 (T7:T0)
Master RX
TA1 (T7:T0)
Master TX
TA2 (T15:T8)
Master RX
TA2 (T15:T8)
DS1923 sets Scratchpad Offset = (T4:T0)
and Clears (PF, AA)
Master RX Ending
Offset with Data
Status (E/S)
DS1923 sets Scratchpad Offset = (T4:T0)
Master TX Data Byte
to Scratchpad Offset
DS1923 sets (E4:E0)
= Scratchpad Offset
Master
TX Reset?
DS1923 Increments Scratchpad Offset
N
Y
Master RX Data Byte
from Scratchpad Offset
Y
Master
TX Reset?
DS1923 Increments Scratchpad Offset
N
Scratchpad Offset =
11111b?
Partial
Byte Written?
Y
Master
TX Reset?
N
Y
N
N
Scratchpad Offset =
11111b?
Y
N
Y
Master
TX Reset?
N
Master
TX Reset?
Master RX "1"s
N
Master RX "1"s
To ROM Functions
Flow Chart (Figure 11)
29 of 53
Y
Master RX CRC16 of
Command, Address Data,
E/S Byte, and Data Starting
at the Target Address
PF = 1
Master RX CRC16 of
Command, Address Data
Y
N
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 9-2. MEMORY/CONTROL FUNCTION FLOW CHART
99H
Copy Scrpd.
[w/PW]
N
Y
Master TX
TA1 (T7:T0), TA2 (T15:T8)
Authorization
Code
Master TX
E/S Byte
Master TX
64-Bits [Password]
N
Password
Accepted?
Y
N
Authorization
Code Match?
Y
AA = 1
DS1923 Copies Scratchpad
Data to Memory
Master
RX "1"s
Master
RX "1"s
N
Copying
Finished
Master
TX Reset?
Y
DS1923 TX "0"
Master
TX Reset?
Y
Y
N
DS1923 TX "1"
N
Master
TX Reset?
Y
30 of 53
N
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 9-3. MEMORY/CONTROL FUNCTION FLOW CHART
69H
Read Mem.
[w/PW]&CRC
N
Y
Master TX
TA1 (T7:T0), TA2 (T15:T8)
Master TX
64-Bits [Password]
Decision made
by DS1923
N
Password
Accepted?
Y
DS1923 sets Memory
Address = (T15:T0)
Decision made
by Master
Master RX Data Byte
from Memory Address
Y
DS1923 Increments Address
Counter
Master
TX Reset?
N
N
End of Page?
Y
Master RX CRC16 of
Command, Address, Data
st
(1 Pass); CRC16 of Data
(Subsequent Passes)
Master TX
Reset
N
CRC OK?
Y
End of
Memory?
N
Y
Master RX "1"s
Master TX
Reset?
Y
31 of 53
N
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 9-4. MEMORY/CONTROL FUNCTION FLOW CHART
96H
Clear Mem.
[w/PW]
55H
Forced
Conversion?
N
Y
Y
Master TX
FFh dummy byte
Master TX
64-Bits [Password]
Master TX
FFh dummy byte
Mission in
Progress?
N
N
Password
Accepted?
DS1923 Performs a
Temp. Conversion
Y
DS1923 copies Result
to Address 020C/Dh
Y
Mission in
Progress?
DS1923 Performs a
Humidity Conversion
N
DS1923 clears Mission
Time Stamp, Mission
Samples Counter,
Alarm Flags
DS1923 copies Result
to Address 020E/Fh
N
DS1923 sets
MEMCLR = 1
Master
TX Reset?
Y
N
N
Master
TX Reset?
Y
32 of 53
Y
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 9-5. MEMORY/CONTROL FUNCTION FLOW CHART
CCH
Start Mission
[w/PW]
33H
Stop Mission
[w/PW]
N
Mission Start
Delay Process
Y
Y
Master TX
64-Bits [Password]
N
Y
Start Delay
Counter = 0?
Master TX
FFh dummy byte
Master TX
64-Bits [Password]
Master TX
FFh dummy byte
N
DS1923 Waits for 1 Minute
Password
Accepted?
Password
Accepted?
DS1923 decrements
Start Delay Counter
Y
Y
N
N
Y
Mission in
Progress?
N
SUTA = 1?
Mission in
Progress?
N
Y
N
N
MEMCLR
= 1?
DS1923 Initiates
Mission Start Delay
Process
DS1923 sets
MIP = 0
WFTA = 0
DS1923 Waits One
Sample Period
Y
DS1923 sets
MIP = 1
MEMCLR = 0
Y
DS1923 Sets WFTA=1
Y
MIP = 0?
Master
TX Reset?
N
DS1923 Performs 8-bit
Temp. Conversion
Y
N
Temp.
Alarm?
Y
DS1923 sets WFTA=0
and logs first sample
The Mission
Sample
Counter will
not increment.
DS1923 Waits One
Sample Period
DS1923 copies RTC
Data to Mission Time
Stamp Register
N
Master
TX Reset?
Y
DS1923 Starts Logging
Taking 1st Sample
End Of Process
33 of 53
If SUTA = 1,
this is the 2nd
sample.
N
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Clear Memory with Password [96h]
The Clear Memory with Password command is used to prepare the device for another mission. This command is
only executed if no mission is in progress. After the command code the master must transmit the 64-bit full-access
password followed by a FFh dummy byte. If passwords are enabled and the transmitted password is different from
the stored full-access password or a mission is in progress, the Clear Memory with Password command will fail.
The device will stop communicating and will wait for a reset pulse. If the password was correct or if passwords
were not enabled, the device will clear the Mission Time Stamp, Mission Sample Counter, and all alarm flags of the
Alarm Status Register. After these cells are cleared, the MEMCLR bit of the General Status Register reads 1 to
indicate the successful execution of the Clear Memory with Password command. Clearing of the data log memory
is not necessary because the Mission Sample Counter indicates how many entries in the data log memory are
valid.
Forced Conversion [55h]
The Forced Conversion command can be used to measure the temperature and humidity without starting a
mission. After the command code the master has to send one FFh byte to get the conversion started. The
conversion result is found as 16-bit value in the Latest Temperature Conversion Result and Latest Humidity
Conversion Result registers. This command is only executed if no mission is in progress (MIP = 0). It cannot be
interrupted and takes maximum 666ms to complete. During this time memory access through the 1-Wire interface
is blocked. The device behaves the same way as during a mission when the sampling interferes with a
memory/control function command. See Memory Access Conflicts for details. A forced conversion must not be
attempted while the RTC oscillator is stopped. This causes the device to enter into an unrecoverable state.
Start Mission with Password [CCh]
The DS1923 uses a control function command to start a mission. A new mission can only be started if the previous
mission has been ended and the memory has been cleared. After the command code, the master must transmit
the 64-bit full-access password followed by a FFh dummy byte. If passwords are enabled and the transmitted
password is different from the stored full-access password or a mission is in progress, the Start Mission with
Password command will fail. The device stops communicating and waits for a reset pulse. If the password was
correct or if passwords were not enabled, the device starts a mission. If SUTA = 0, the sampling begins as soon as
the mission start delay is over. If SUTA = 1, the first sample is written to the data log memory at the time the
temperature alarm occurred. However, the Mission Sample Counter does not increment. One sample period later,
the Mission Time Stamp will be set and the regular sampling and logging begins. While the device is waiting for a
temperature alarm to occur, the WFTA flag in the general status register will read 1. During a mission there is only
read access to the Register Pages.
Stop Mission with Password [33h]
The DS1923 uses a control function command to stop a mission. Only a mission that is in progress can be
stopped. After the command code, the master must transmit the 64-bit full-access password followed by a FFh
dummy byte. If passwords are enabled and the transmitted password is different from the stored full-access
password or a mission is not in progress, the Stop Mission with Password command will fail. The device stops
communicating and waits for a reset pulse. If the password was correct or if passwords were not enabled, the
device clears the MIP bit in the General Status Register and restore write access to the Register Pages. The
WFTA bit is not cleared. See the description of the General Status Register for a method to clear the WFTA bit.
MEMORY ACCESS CONFLICTS
While a mission is in progress or while the device is waiting for a temperature alarm to start a mission, periodically
a temperature and/or humidity sample is taken and logged. This "internal activity" has priority over 1-Wire
communication. As a consequence, device-specific commands (excluding ROM function commands and 1-Wire
reset) will not perform properly when internal and "external" activities interfere with each other. Not affected are the
commands Start Mission, Forced Conversion, and Clear Memory because they are not applicable while a mission
is in progress or while the device is waiting for a temperature alarm. The table below explains how the remaining
five commands are affected by internal activity, how to detect this interference and how to work around it.
34 of 53
Command
Write Scratchpad
Read Scratchpad
Copy Scratchpad
Read Memory with
CRC
Stop Mission
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Indication of Interference
Remedy
Wait 0.5 seconds, 1-Wire reset, address the device,
repeat Write Scratchpad with the same data, and
The CRC16 at the end of the
check the validity of the CRC16 at the end of the
command flow reads FFFFh.
command flow. Alternatively, use Read Scratchpad to
verify data integrity.
The data read changes to FFh
Wait 0.5 seconds, 1-Wire reset, address the device,
bytes or all bytes received are
repeat Read Scratchpad, and check the validity of the
FFh, including the CRC at the
CRC16 at the end of the command flow.
end of the command flow.
The device behaves as if
Wait 0.5 seconds, 1-Wire reset, address the device,
authorization code or password issue Read Scratchpad and check the AA-bit of the
was not valid or as if the copy
E/S byte. If the AA-bit is set, Copy Scratchpad was
function would not end.
successful.
The data read changes to all
FFh bytes or all bytes received Wait 0.5 seconds, 1-Wire reset, address the device,
are FFh, including the CRC at
repeat Read Memory with CRC, and check the validity
the end of the command flow,
of the CRC16 at the end of the memory page.
despite a valid password.
Wait 0.5 seconds, 1-Wire reset, address the device,
The general Status register at
and repeat Stop Mission. Perform a 1-Wire reset,
address 215h reads FFh or the
address the device, read the general Status register at
MIP bit is 1 while bits 0, 2, and
address 215h and check the MIP-bit. If the MIP-bit is 0,
5 are 0.
Stop Mission was successful.
The interference is more likely to be seen with a high sample rate (1 sample every second) and with high-resolution
logging, which can last up to 666ms when both temperature and humidity are recorded. With lower sample rates
interference may hardly be visible at all. In any case, when writing driver software, it is important to know about the
possibility of interference and to take measures to work around it.
1-WIRE BUS SYSTEM
The 1-Wire bus is a system, which has a single bus master and one or more slaves. In all instances the DS1923 is
a slave device. The bus master is typically a microcontroller. The discussion of this bus system is broken down into
three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing). The
1-Wire protocol defines bus transactions in terms of the bus state during specific time slots that are initiated on the
falling edge of sync pulses from the bus master. For a more detailed protocol description, refer to Chapter 4 of the
Book of DS19xx iButton Standards.
HARDWARE CONFIGURATION
The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to drive it at
the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have open drain or tri-state
outputs. The 1-Wire port of the DS1923 is open-drain with an internal circuit equivalent to that shown in Figure 10.
A multidrop bus consists of a 1-Wire bus with multiple slaves attached. At standard speed the 1-Wire bus has a
maximum data rate of 16.3kbps. The speed can be boosted to 142kbps by activating the Overdrive mode. The
DS1923 is not guaranteed to be fully compliant to the iButton Standard. Its maximum data rate in standard speed
mode is 15.4kbps and 125kbps in Overdrive. The value of the pullup resistor primarily depends on the network size
and load conditions. The DS1923 requires a pullup resistor of maximum 2.2kΩ at any speed.
The idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus MUST be
left in the idle state if the transaction is to resume. If this does not occur and the bus is left low for more than 16µs
(Overdrive speed) or more than 120µs (standard speed), one or more devices on the bus may be reset. Note that
the DS19233 does not quite meet the full 16µs maximum low time of the normal 1-Wire bus Overdrive timing. With
the DS1923 the bus must be left low for no longer than 12µs at Overdrive to ensure that no DS1923 on the 1-Wire
bus performs a reset. The DS1923 communicates properly when used in conjunction with a DS2480B or DS2490
1-Wire driver and adapters that are based on these driver chips.
35 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 10. HARDWARE CONFIGURATION
BUS MASTER
VPUP
DS1923 1-Wire PORT
RPUP
RX
DATA
TX
RX = RECEIVE
Open Drain
Port Pin
RX
TX
5 µA
Typ.
TX = TRANSMIT
100 Ω
MOSFET
TRANSACTION SEQUENCE
The protocol for accessing the DS1923 through the 1-Wire port is as follows:
ƒ
ƒ
ƒ
ƒ
Initialization
ROM Function Command
Memory/Control Function Command
Transaction/Data
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a
reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the slave(s). The presence
pulse lets the bus master know that the DS1923 is on the bus and is ready to operate. For more details, see the
1-Wire Signaling section.
1-Wire ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the eight ROM function commands that the
DS1923 supports. All ROM function commands are 8 bits long. A list of these commands follows (refer to flowchart
in Figure 11).
Read ROM [33h]
This command allows the bus master to read the DS1923’s 8-bit family code, unique 48-bit serial number, and 8-bit
CRC. This command can only be used if there is a single slave on the bus. If more than one slave is present on the
bus, a data collision occurs when all slaves try to transmit at the same time (open-drain produces a wired-AND
result). The resultant family code and 48-bit serial number results in a mismatch of the CRC.
Match ROM [55h]
The Match ROM command, followed by a 64-bit ROM sequence, allows the bus master to address a specific
DS1923 on a multidrop bus. Only the DS1923 that exactly matches the 64-bit ROM sequence responds to the
following memory function command. All other slaves will wait for a reset pulse. This command can be used with a
single or multiple devices on the bus.
Search ROM [F0h]
When a system is initially brought up, the bus master might not know the number of devices on the 1-Wire bus or
their registration numbers. By taking advantage of the wired-AND property of the bus, the master can use a
process of elimination to identify the registration numbers of all slave devices. For each bit of the registration
number, starting with the least significant bit, the bus master issues a triplet of time slots. On the first slot, each
slave device participating in the search outputs the true value of its registration number bit. On the second slot,
each slave device participating in the search outputs the complemented value of its registration number bit. On the
third slot, the master writes the true value of the bit to be selected. All slave devices that do not match the bit
written by the master stop participating in the search. If both of the read bits are zero, the master knows that slave
36 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
devices exist with both states of the bit. By choosing which state to write, the bus master branches in the romcode
tree. After one complete pass, the bus master knows the registration number of a single device. Additional passes
identify the registration numbers of the remaining devices. Refer to App Note 187: 1-Wire Search Algorithm for a
detailed discussion, including an example.
Conditional Search [ECh]
The Conditional Search ROM command operates similarly to the Search ROM command except that only those
devices, which fulfill certain conditions, participate in the search. This function provides an efficient means for the
bus master to identify devices on a multidrop system that have to signal an important event. After each pass of the
conditional search that successfully determined the 64-bit ROM code for a specific device on the multidrop bus,
that particular device can be individually accessed as if a Match ROM had been issued, since all other devices
have dropped out of the search process and will be waiting for a reset pulse.
The DS1923 responds to the conditional search if one of the five alarm flags of the Alarm Status Register (address
0214h) reads 1. The humidity and temperature alarm only occurs if enabled (see Temperature Sensor Alarm and
Humidity Alarm). The BOR alarm is always enabled. The first alarm that occurs makes the device respond to the
Conditional Search command.
Skip ROM [CCh]
This command can save time in a single-drop bus system by allowing the bus master to access the memory
functions without providing the 64-bit ROM code. If more than one slave is present on the bus and, for example, a
Read command is issued following the Skip ROM command, data collision occurs on the bus as multiple slaves
transmit simultaneously (open-drain pulldowns produce a wired-AND result).
Resume Command [A5h]
The DS1923 needs to be accessed several times before a mission starts. In a multidrop environment this means
that the 64-bit ROM code after a Match ROM command has to be repeated for every access. To maximize the data
throughput in a multidrop environment, the Resume function was implemented. This function checks the status of
the RC bit and, if it is set, directly transfers control to the Memory/Control functions, similar to a Skip ROM
command. The only way to set the RC bit is through successfully executing the Match ROM, Search ROM or
Overdrive Match ROM command. Once the RC bit is set, the device can repeatedly be accessed through the
Resume Command function. Accessing another device on the bus will clear the RC bit, preventing two or more
devices from simultaneously responding to the Resume Command function.
Overdrive Skip ROM [3Ch]
On a single-drop bus this command can save time by allowing the bus master to access the memory/control functions without providing the 64-bit ROM code. Unlike the normal Skip ROM command, the Overdrive Skip ROM sets
the DS1923 in the Overdrive mode (OD = 1). All communication following this command has to occur at Overdrive
speed until a reset pulse of minimum 690µs duration resets all devices on the bus to standard speed (OD = 0).
When issued on a multidrop bus this command will set all Overdrive-supporting devices into Overdrive mode. To
subsequently address a specific Overdrive-supporting device, a reset pulse at Overdrive speed has to be issued
followed by a Match ROM or Search ROM command sequence. This speeds up the time for the search process. If
more than one slave supporting Overdrive is present on the bus and the Overdrive Skip ROM command is followed
by a Read command, data collision occurs on the bus as multiple slaves transmit simultaneously (open-drain
pulldowns will produce a wired-AND result).
Overdrive Match ROM [69h]
The Overdrive Match ROM command followed by a 64-bit ROM sequence transmitted at Overdrive Speed allows
the bus master to address a specific DS1923 on a multidrop bus and to simultaneously set it in Overdrive mode.
Only the DS1923 that exactly matches the 64-bit ROM sequence will respond to the subsequent memory/control
function command. Slaves already in Overdrive mode from a previous Overdrive Skip or successful Overdrive
Match command remains in Overdrive mode. All overdrive-capable slaves return to standard speed at the next
Reset Pulse of minimum 690µs duration. The Overdrive Match ROM command can be used with a single or
multiple devices on the bus.
37 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 11-1. ROM FUNCTIONS FLOW CHART
Bus Master TX
Reset Pulse
From Memory Functions
Flow Chart (Figure 9)
nd
From Figure 11, 2
OD
Reset Pulse?
Part
N
OD = 0
Y
Bus Master TX ROM
Function Command
33h
Read ROM
Command?
Y
RC = 0
DS1923 TX
Presence Pulse
N
55h
Match ROM
Command?
To Figure 11
nd
2 Part
F0h
Search ROM
Command?
N
Y
ECh
Cond. Search
Command?
N
Y
RC = 0
N
Y
RC = 0
RC = 0
N
Condition Met?
Y
DS1923 TX
Family Code
(1 Byte)
Master TX Bit 0
N
Bit 0
Match?
N
N
Bit 0
Match?
N
N
Bit 1
Match?
Y
Y
DS1923 TX Bit 63
DS1923 TX Bit 63
Master TX Bit 63
DS1923 TX Bit 63
DS1923 TX Bit 63
Master TX Bit 63
Master TX Bit 63
N
Bit 63
Match?
DS1923 TX Bit 1
DS1923 TX Bit 1
Master TX Bit 1
N
Bit 1
Match?
Y
DS1923 TX
CRC Byte
Y
DS1923 TX Bit 1
DS1923 TX Bit 1
Master TX Bit 1
Master TX Bit 1
Bit 1
Match?
Bit 0
Match?
Y
Y
DS1923 TX
Serial Number
(6 Bytes)
DS1923 TX Bit 0
DS1923 TX Bit 0
Master TX Bit 0
DS1923 TX Bit 0
DS1923 TX Bit 0
Master TX Bit 0
N
N
Bit 63
Match?
Y
Bit 63
Match?
Y
RC = 1
RC = 1
To Memory Functions
Flow Chart (Figure 9)
38 of 53
Y
RC = 1
To Figure 11
nd
2 Part
From Figure 11
nd
2 Part
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 11-2. ROM FUNCTIONS FLOW CHART
st
To Figure 11, 1 Part
From Figure 11
st
1 Part
CCh
Skip ROM
Command?
Y
N
A5h
Resume
Command?
3Ch
Overdrive
Skip ROM?
N
Y
N
Y
RC = 0
Y
RC = 0 ; OD = 1
RC = 1 ?
69h
N
Overdrive Match
ROM?
RC = 0 ; OD = 1
N
Master TX Bit 0
Y
Master
TX Reset ?
Y
N
Bit 0
Match?
Y
N
Master TX Bit 1
Master
TX Reset ?
Y
N
Bit 1
Match?
Y
N
Master TX Bit 63
N
Bit 63
Match?
Y
From Figure 11
st
1 Part
RC = 1
To Figure 11
st
1 Part
39 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
1-WIRE SIGNALING
The DS1923 requires strict protocols to ensure data integrity. The protocol consists of four types of signaling on
one line: Reset Sequence with Reset Pulse and Presence Pulse, Write-Zero, Write-One and Read-Data. Except for
the presence pulse the bus master initiates all these signals. The DS1923 can communicate at two different
speeds, standard speed and Overdrive Speed. If not explicitly set into the Overdrive mode, the DS1923
communicates at standard speed. While in Overdrive Mode the fast timing applies to all waveforms.
To get from idle to active, the voltage on the 1-Wire line needs to fall from VPUP below the threshold VTL. To get
from active to idle, the voltage needs to rise from VILMAX past the threshold VTH. The time it takes for the voltage to
make this rise is seen in Figure 12 as 'ε' and its duration depends on the pullup resistor (RPUP) used and the
capacitance of the 1-Wire network attached. The voltage VILMAX is relevant for the DS1923 when determining a
logical level, not triggering any events.
The initialization sequence required to begin any communication with the DS1923 is shown in Figure 12. A Reset
Pulse followed by a Presence Pulse indicates the DS1923 is ready to receive data, given the correct ROM and
memory function command. If the bus master uses slew-rate control on the falling edge, it must pull down the line
for tRSTL + tF to compensate for the edge. A tRSTL duration of 690µs or longer will exit the Overdrive Mode returning
the device to standard speed. If the DS1923 is in Overdrive Mode and tRSTL is no longer than 80µs the devices
remain in Overdrive Mode.
Figure 12. INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES”
MASTER TX “RESET PULSE” MASTER RX “PRESENCE PULSE”
tMSP
ε
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
tF
tRSTL
RESISTOR
tPDH
MASTER
tPDL
tRSTH
tREC
DS1923
After the bus master has released the line it goes into receive mode (RX). Now the 1-Wire bus is pulled to VPUP
through the pullup resistor or, in case of a DS2480B driver, by active circuitry. When the threshold VTH is crossed,
the DS1923 waits for tPDH and then transmits a Presence Pulse by pulling the line low for tPDL. To detect a presence
pulse, the master must test the logical state of the 1-Wire line at tMSP.
The tRSTH window must be at least the sum of tPDHMAX, tPDLMAX, and tRECMIN. Immediately after tRSTH is expired, the
DS1923 is ready for data communication. In a mixed population network tRSTH should be extended to minimum
480µs at standard speed and 48µs at Overdrive speed to accommodate other 1-Wire devices.
Read/Write Time Slots
Data communication with the DS1923 takes place in time slots, which carry a single bit each. Write time slots
transport data from bus master to slave. Read time slots transfer data from slave to master. The definitions of the
write and read time slots are illustrated in Figure 13.
All communication begins with the master pulling the data line low. As the voltage on the 1-Wire line falls below the
threshold VTL, the DS1923 starts its internal timing generator that determines when the data line is sampled during
a write time slot and how long data will be valid during a read-time slot.
40 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Master-to-Slave
For a write-one time slot, the voltage on the data line must have crossed the VTH threshold before the write-one
low time tW1LMAX is expired. For a write-zero time slot, the voltage on the data line must stay below the VTH
threshold until the write-zero low time tW0LMIN is expired. The voltage on the data line should not exceed VILMAX
during the entire tW0L or tW1L window. After the VTH threshold has been crossed, the DS1923 needs a recovery time
tREC before it is ready for the next time slot.
Figure 13. READ/WRITE TIMING DIAGRAM
Write-One Time Slot
tW1L
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
ε
tF
tSLOT
RESISTOR
MASTER
Write-Zero Time Slot
tW0L
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
tF
tSLOT
RESISTOR
tREC
MASTER
Read-Data Time Slot
tMSR
tRL
VPUP
VIHMASTER
VTH
Master
Sampling
Window
VTL
VILMAX
0V
δ
tF
tREC
tSLOT
RESISTOR
MASTER
41 of 53
DS1923
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Slave-to-Master
A read-data time slot begins like a write-one time slot. The voltage on the data line must remain below VTL until the
read-low time tRL is expired. During the tRL window, when responding with a 0, the DS1923 starts pulling the data
line low; its internal timing generator determines when this pulldown ends and the voltage starts rising again. When
responding with a 1, the DS1923 does not hold the data line low at all, and the voltage starts rising as soon as tRL
is over.
The sum of tRL + δ (rise rime) on one side and the internal timing generator of the DS1923 on the other side define
the master sampling window (tMSRMIN to tMSRMAX) in which the master must perform a read from the data line. For
most reliable communication, tRL should be as short as permissible and the master should read close to but no later
than tMSRMAX. After reading from the data line, the master must wait until tSLOT is expired. This guarantees sufficient
recovery time tREC for the DS1923 to get ready for the next time slot.
Improved Network Behavior
In a 1-Wire environment line termination is possible only during transients controlled by the bus master (1-Wire
driver). 1-Wire networks, therefore are susceptible to noise of various origins. Depending on the physical size and
topology of the network, reflections from end points and branch points can add up or cancel each other to some
extent. Such reflections are visible as glitches or ringing on the 1-Wire communication line. Noise coupled onto the
1-Wire line from external sources can also result in signal glitching. A glitch during the rising edge of a time slot can
cause a slave device to lose synchronization with the master and, as a consequence, result in a search ROM
command coming to a dead end or cause a device-specific function command to abort. For better performance in
network applications, the DS1923 uses a new 1-Wire front end, which makes it less sensitive to noise and also
reduces the magnitude of noise injected by the slave device itself.
The 1-Wire front end of the DS1923 differs from traditional slave devices in four characteristics.
1) The falling edge of the presence pulse has a controlled slew rate. This provides a better match to the line
impedance than a digitally switched transistor, converting the high-frequency ringing known from traditional
devices into a smoother low-bandwidth transition. The slew-rate control is specified by the parameter tFPD,
which has different values for standard and Overdrive speed.
2) There is additional low-pass filtering in the circuit that detects the falling edge at the beginning of a time slot.
This reduces the sensitivity to high-frequency noise. This additional filtering does not apply at Overdrive speed.
3) There is a hysteresis at the low-to-high switching threshold VTH. If a negative glitch crosses VTH but does not go
below VTH - VHY, it will not be recognized (Figure 14, Case A). The hysteresis is effective at any 1-Wire speed.
4) There is a time window specified by the rising edge hold-off time tREH during which glitches are ignored, even if
they extend below VTH - VHY threshold (Figure 14, Case B, tGL < tREH). Deep-voltage droops or glitches that
appear late after crossing the VTH threshold and extend beyond the tREH window cannot be filtered out and are
taken as beginning of a new time slot (Figure 14, Case C, tGL ≥ tREH).
Only devices that have the parameters tFPD, VHY, and tREH specified in their electrical characteristics use the
improved 1-Wire front end.
Figure 14. NOISE SUPPRESSION SCHEME
tREH
VPUP
tREH
VTH
VHY
Case A
Case B
Case C
0V
tGL
42 of 53
tGL
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
CRC GENERATION
With the DS1923 there are two different types of CRCs (Cyclic Redundancy Checks). One CRC is an 8-bit type
and is stored in the most significant byte of the 64-bit ROM. The bus master can compute a CRC value from the
first 56 bits of the 64-bit ROM and compare it to the value stored within the DS1923 to determine if the ROM data
has been received error-free. The equivalent polynomial function of this CRC is: X8 + X5 + X4 + 1. This 8-bit CRC is
received in the true (noninverted) form. It is computed at the factory and lasered into the ROM.
The other CRC is a 16-bit type, generated according to the standardized CRC16-polynomial function x16 + x15 + x2
+ 1. This CRC is used for error detection when reading register pages or the data log memory using the Read
Memory with CRC command and for fast verification of a data transfer when writing to or reading from the
scratchpad. In contrast to the 8-bit CRC, the 16-bit CRC is always communicated in the inverted form. A CRC
generator inside the DS1923 (Figure 15) calculates a new 16-bit CRC as shown in the command flow chart of
Figure 9. The bus master compares the CRC value read from the device to the one it calculates from the data and
decides whether to continue with an operation or to reread the portion of the data with the CRC error. With the
initial pass through the Read Memory with CRC flow chart, the 16-bit CRC value is the result of shifting the
command byte into the cleared CRC generator, followed by the 2 address bytes and the data bytes. The password
is excluded from the CRC calculation. Subsequent passes through the Read Memory with CRC flow chart generate
a 16-bit CRC that is the result of clearing the CRC generator and then shifting in the data bytes.
With the Write Scratchpad command the CRC is generated by first clearing the CRC generator and then shifting in
the command code, the Target Addresses, TA1 and TA2, and all the data bytes. The DS1923 transmits this CRC
only if the data bytes written to the scratchpad include scratchpad ending offset 11111b. The data can start at any
location within the scratchpad.
With the Read Scratchpad command the CRC is generated by first clearing the CRC generator and then shifting in
the command code, the Target Addresses, TA1 and TA2, the E/S byte, and the scratchpad data starting at the
target address. The DS1923 transmits this CRC only if the reading continues through the end of the scratchpad,
regardless of the actual ending offset. For more information on generating CRC values see the Dallas Application
Note 27.
Figure 15. CRC-16 HARDWARE DESCRIPTION AND POLYNOMIAL
16
Polynomial = X
st
nd
1
STAGE
0
th
8
2
X
th
10
STAGE
9
X
10
X
11
X
12
X
13
X
8
STAGE
7
X
th
14
STAGE
X
th
7
STAGE
6
X
th
13
STAGE
th
6
STAGE
5
X
th
12
STAGE
th
5
STAGE
4
X
th
11
STAGE
2
+X +1
th
4
STAGE
3
X
th
9
STAGE
th
3
STAGE
1
X
X
rd
2
STAGE
15
+X
th
15
STAGE
14
X
16
STAGE
15
X
INPUT DATA
43 of 53
16
X
CRC
OUTPUT
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Command-Specific 1-Wire Communication Protocol—Legend
Symbol
Description
RST
PD
Select
WS
RS
CPS
RMC
CM
FC
SM
STP
TA
TA-E/S
<data to EOS>
<data to EOP>
<data to EOM>
<PW/dummy>
<32 bytes>
<data>
FFh
CRC16\
FF loop
AA loop
1-Wire Reset Pulse generated by master
1-Wire Presence Pulse generated by slave
Command and data to satisfy the ROM function protocol
Command "Write Scratchpad"
Command "Read Scratchpad"
Command "Copy Scratchpad with Password"
Command "Read Memory with Password & CRC"
Command "Clear Memory with Password "
Command "Forced Conversion"
Command "Start Mission with Password"
Command "Stop Mission with Password"
Target Address TA1, TA2
Target Address TA1, TA2 with E/S byte
Transfer of as many data bytes as are needed to reach the scratchpad offset 1Fh
Transfer of as many data bytes as are needed to reach the end of a memory page
Transfer of as many data bytes as are needed to reach the end of the data log memory
Transfer of 8 bytes that either represent a valid password or acceptable dummy data
Transfer of 32 bytes
Transfer of an undetermined amount of data
Transmission of one byte FFh
Transfer of an inverted CRC16
Indefinite loop where the master reads FF bytes
Indefinite loop where the master reads AA bytes
Command-Specific 1-Wire Communication Protocol—Color Codes
Master to slave
Slave to master
Write Scratchpad, Reaching the End of the Scratchpad (Cannot Fail)
RST
PD
Select
WS
TA
<data to EOS>
CRC16\
FF loop
Read Scratchpad (Cannot Fail)
RST
PD
Select
RS
TA-E/S
<data to EOS>
CRC16\
Copy Scratchpad with Password (Success)
RST
PD
Select
CPS
TA-E/S
<PW/dummy>
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AA loop
FF loop
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Copy Scratchpad with Password (Fail TA-E/S or Password)
RST
PD
Select
CPS
TA-E/S
<PW/dummy>
FF loop
Read Memory with Password and CRC (Success)
RST
PD
Select
RMC
TA
<PW/dummy>
<data to EOP>
CRC16\
<32 bytes>
CRC16\
FF loop
Loop
Read Memory with Password and CRC (Fail Password or Address)
RST
PD
Select
RMC
TA
<PW/dummy>
FF loop
Clear Memory with Password
RST
PD
Select
CM
<PW/dummy>
FFh
FF loop
To verify success, read the General Status Register at address 0215h. If MEMCLR is 1, the command was
executed successfully.
Forced Conversion
RST
PD
Select
FC
FFh
FF loop
To read the result and to verify success, read the addresses 020Ch to 020Fh (results) and the Device Sample
Counter at address 0223h to 0225h. If the count has incremented, the command was executed successfully.
Start Mission with Password
RST
PD
Select
SM
<PW/dummy>
FFh
FF loop
To verify success, read the General Status Register at address 0215h. If MIP is 1 and MEMCLR is 0, the command
was executed successfully.
Stop Mission with Password
RST
PD
Select
STP
<PW/dummy>
FFh
FF loop
To verify success, read the General Status Register at address 0215h. If MIP is 0, the command was executed
successfully.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
MISSION EXAMPLE: PREPARE AND START A NEW MISSION
Assumption: The previous mission has been ended by using the Stop Mission command. Passwords are not
enabled. The device is a DS1923.
Starting a mission requires three steps:
Step 1: clear the data of the previous mission
Step 2: write the setup data to register page 1
Step 3: start the mission
STEP 1
Clear the previous mission.
With only a single device connected to the bus master, the communication of step 1 looks like this:
MASTER MODE
TX
RX
TX
TX
TX
TX
TX
RX
DATA (LSB FIRST)
(Reset)
(Presence)
CCh
96h
<8 FFh bytes>
FFh
(Reset)
(Presence)
COMMENTS
Reset pulse
Presence pulse
Issue “skip ROM” command
Issue “clear memory” command
Send dummy password
Send dummy byte
Reset pulse
Presence pulse
STEP 2
During the setup, the device needs to learn the following information:
ƒ Time and Date
ƒ Sample Rate
ƒ Alarm Thresholds
ƒ Alarm Controls (Response to Conditional Search)
ƒ General Mission Parameters (e.g., Channels to Log and Logging Format, Rollover, Start Mode)
ƒ Mission Start Delay
The following data will setup the DS1923 for a mission that logs temperature and humidity using 8-bit format for
both. Such a mission could last up to 28 days until the 8192-byte data log memory is full.
ADDRESS
0200h
0201h
0202h
0203h
0204h
0205h
0206h
0207h
0208h
0209h
020Ah
020Bh
020Ch
020Dh
020Eh
020Fh
DATA
00h
30h
15h
15h
05h
04h
0Ah
00h
66h
7Ah
6Fh
9Eh
FFh
FFh
FFh
FFh
EXAMPLE VALUES
FUNCTION
15:30:00 hours
Time
15th of May in 2004
Date
Every 10 minutes (EHSS = 0)
Sample rate
10°C low
20°C high
40%RH low
70%RH high
Temperature alarm
Threshold
Humidity alarm threshold,
No software correction used
(don’t care)
Clock through
Read-only registers
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ADDRESS
0210h
0211h
0212h
0213h
0214h
0215h
0216h
0217h
0218h
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
DATA
EXAMPLE VALUES
FUNCTION
03h
Enable high and low alarm
Temperature Alarm Control
FFh
Enable high and low alarm
Humidity Alarm Control
01h
On (enabled), EHSS = 0 (low sample rate)
RTC oscillator control, sample rate
selection
C3h
Normal start; no rollover; 8-bit logging
General mission control
FFh
(don’t care)
Clock through
FFh
Read-only registers
5Ah
00h
90 minutes
Mission start delay
00h
With only a single device connected to the bus master, the communication of step 2 looks like this:
MASTER MODE
TX
RX
TX
TX
TX
TX
TX
TX
TX
RX
TX
TX
RX
RX
RX
RX
TX
RX
TX
TX
TX
TX
TX
TX
TX
RX
DATA (LSB FIRST)
(Reset)
(Presence)
CCh
0Fh
00h
02h
<25 data bytes>
<7 FFh bytes>
(Reset)
(Presence)
CCh
AAh
00h
02h
1Fh
<32 data bytes>
(Reset)
(Presence)
CCh
99h
00h
02h
1Fh
<8 FFh bytes>
(Reset)
(Presence)
47 of 53
COMMENTS
Reset pulse
Presence pulse
Issue “skip ROM” command
Issue “write scratchpad” command
TA1, beginning offset=00h
TA2, address=0200h
Write 25 bytes of data to scratchpad
Write through the end of the scratchpad
Reset pulse
Presence pulse
Issue “skip ROM” command
Issue “read scratchpad” command
Read TA1, beginning offset=00h
Read TA2, address=0200h
Read E/S, ending offset=1Fh, flags=0h
Read scratchpad data and verify
Reset pulse
Presence pulse
Issue “skip ROM” command
Issue “copy scratchpad” command
TA1
TA2
(AUTHORIZATION CODE)
E/S
Send dummy password
Reset pulse
Presence pulse
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
STEP 3
Start the new mission.
With only a single device connected to the bus master, the communication of step 3 looks like this:
MASTER MODE
DATA (LSB FIRST)
COMMENTS
TX
(Reset)
Reset pulse
RX
(Presence)
Presence pulse
TX
CCh
Issue “skip ROM” command
TX
CCh
Issue “start mission” command
TX
<8 FFh bytes>
Send dummy password
TX
FFh
Send dummy byte
TX
(Reset)
Reset pulse
RX
(Presence)
Presence pulse
If step 3 was successful, the MIP bit in the General Status Register will be 1, the MEMCLR bit will be 0 and the
mission start delay will count down.
SOFTWARE CORRECTION ALGORITHM FOR TEMPERATURE
The accuracy of high-resolution temperature conversion results (forced conversion as well as temperature logs)
can be improved through a correction algorithm. The data needed for this software correction is stored in the
calibration memory (memory page 18). It consists of reference temperature (Tr) and conversion result (Tc) for two
different temperatures, as shown below. See section Temperature Conversion for the binary number format.
ADDRESS
0240h
0241h
0242h
0243h
0244h
0245h
0246h
0247h
DESIGNATOR
Tr2H
Tr2L
Tc2H
Tc2L
Tr3H
Tr3L
Tc3H
Tc3L
DESCRIPTION
Cold reference temperature, high-byte
Cold reference temperature, low-byte
Conversion result at cold reference temperature, high-byte
Conversion result at cold reference temperature, low-byte
Hot reference temperature, high-byte
Hot reference temperature, low-byte
Conversion result at hot reference temperature, high-byte
Conversion result at hot reference temperature, low-byte
The software correction algorithm requires two additional values, which are not stored in the device. For the
DS1923 these values are Tr1 = 60°C and Offset = 41.
The correction algorithm consists of two steps, preparation and execution. The preparation step first converts
temperature data from binary to decimal °C format. Next three coefficients A, B, and C are computed. In the
execution step the temperature reading as delivered by the DS1923 is first converted from the low/high-byte format
(TcL, TcH) to °C (Tc) and then corrected to Tcorr. Once step 1 is performed, the three coefficients can be used
repeatedly to correct any temperature reading and temperature log of the same device.
Step 1. Preparation
Tr1 = 60
Offset = 41
Tr2 = Tr2H/2 + Tr2L/512 - Offset
(convert from binary to °C)
Tr3 = Tr3H/2 + Tr3L/512 - Offset
(convert from binary to °C)
Tc2 = Tc2H/2 + Tc2L/512 - Offset
(convert from binary to °C)
Tc3 = Tc3H/2 + Tc3L/512 - Offset
(convert from binary to °C)
Err2 = Tc2 - Tr2
Err3 = Tc3 - Tr3
Err1 = Err2
B = (Tr22 - Tr12) * (Err3 - Err1)/[(Tr22 - Tr12) * (Tr3 - Tr1) + (Tr32 - Tr12) * (Tr1 - Tr2)]
A = B * (Tr1 – Tr2) / (Tr22 - Tr12)
C = Err1 - A * Tr12 - B * Tr1
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Step 2. Execution
Tc = TcH/2 + TcL/512 - Offset
Tcorr = Tc - (A * Tc2 + B * Tc + C)
(convert from binary to °C)
(the actual correction)
Numerical Correction Example
Converted Data from Calibration Memory
Tr2 = -10.1297°C
Tr3 = 24.6483°C
Tc2 = -10.0625°C
Tc3 = 24.5°C
Resulting Correction Coefficients
B = -0.008741
A = 0.000175/°C
C = -0.039332°C
Error Values
Err2 = 0.0672°C
Err3 = -0.1483°C
Err1 = Err2
Application of Correction Coefficients to Sample Reading
Tc = 22.500000°C
Tcorr = 22.647275°C
NOTE: The software correction requires floating point arithmetic (24-bit or better). Suitable math libraries for
microcontrollers are found on various websites and are included in cross-compilers.
SOFTWARE CORRECTION ALGORITHM FOR HUMIDITY
The accuracy of humidity conversion results (forced conversion as well as logged data) can be improved through a
correction algorithm. The data needed for this software correction is stored in the calibration memory (memory
page 18). It consists of reference humidity (Hr) and conversion result (Hc) for three different humidity levels, as
shown below. The data is taken at 25°C.
Address
0248h
0249h
024Ah
024Bh
024Ch
024Dh
024Eh
024Fh
0250h
0251h
0252h
0253h
Designator
Hr1H
Hr1L
Hc1H
Hc1L
Hr2H
Hr2L
Hc2H
Hc2L
Hr3H
Hr3L
Hc3H
Hc3L
Description
Low reference humidity, high-byte
Low reference humidity, low-byte
Conversion result at low reference humidity, high-byte
Conversion result at low reference humidity, low-byte
Medium reference humidity, high-byte
Medium reference humidity, low-byte
Conversion result at medium reference humidity, high-byte
Conversion result at medium reference humidity, low-byte
High reference humidity, high-byte
High reference humidity, low-byte
Conversion result at high reference humidity, high-byte
Conversion result at high reference humidity, low-byte
The correction algorithm consists of two steps: preparation and execution. The preparation step first converts
humidity data from binary to decimal %RH format. Next three coefficients A, B, and C are computed. In the
execution step the humidity reading as delivered by the DS1923 (raw data) is first converted from the low/high-byte
format (HcL, HcH) to %RH (Hc) and then corrected to Hcorr. Once step 1 is performed, the three coefficients can
be used repeatedly to correct any humidity reading and humidity log of the same device.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Step 1. Preparation
For the humidity data in the calibration memory, the lower four bits of each low byte are set to 0. This simplifies the
conversion from the binary data format to raw %RH values to a one-line equation.
Hr1 = ((Hr1H * 256 + Hr1L) * 5.02/65536 - 0.958)/0.0307
Hr2 = ((Hr2H * 256 + Hr2L) * 5.02/65536 - 0.958)/0.0307
Hr3 = ((Hr3H * 256 + Hr3L) * 5.02/65536 - 0.958)/0.0307
Hc1 = ((Hc1H * 256 + Hc1L) * 5.02/65536 - 0.958)/0.0307
Hc2 = ((Hc2H * 256 + Hc2L) * 5.02/65536 - 0.958)/0.0307
Hc3 = ((Hc3H * 256 + Hc3L) * 5.02/65536 - 0.958)/0.0307
(convert from binary to %RH)
Err1 = Hc1 - Hr1
Err2 = Hc2 - Hr2
Err3 = Hc3 - Hr3
B=
A=
C=
2
2
2
2
2
[(Hr2 - Hr1 ) * (Err3 - Err1) + Hr3²*(Err1 - Err2) + Hr1² * (Err2 - Err1)]/[(Hr2 - Hr1 ) * (Hr3 - Hr1) + (Hr3 2
Hr1 ) * (Hr1 - Hr2)]
[Err2 - Err1 + B * (Hr1 - Hr2)] / (Hr22 - Hr12)
Err1 - A * Hr12 - B * Hr1
Step 2. Execution
Hc = ((HcH * 256 + HcL) * 5.02/65536 - 0.958)/0.0307
Hcorr = Hc - (A * Hc2 + B * Hc + C)
(convert from binary to %RH)
(the actual correction)
Numerical Correction Example
Converted Data from Calibration Memory
Hr1 = 20%RH
Hr2 = 60%RH
Hr3 = 90%RH
Hc1 = 17.65%RH
Hc2 = 56.41%RH
Hc3 = 89.57%RH
Resulting Correction Coefficients
B = -0.186810
A = 0.001948/%RH
C = 0.607143%RH
Error Values
Err1 = -2.35%RH
Err2 = -3.59%RH
Err3 = -0.43%RH
Application of Correction Coefficients to Sample Reading
Hc = 8.9%RH
Hcorr = 9.8%RH
NOTE: The software correction requires floating point arithmetic (24-bit or better). Suitable math libraries for
microcontrollers are found on various websites and are included in cross-compilers.
50 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
RH TEMPERATURE COMPENSATION
The data for the software correction of humidity is taken at 25°C. Since the temperature characteristics of the
humidity sensor are known, humidity readings taken at other temperatures can be corrected, provided the
temperature at the time of the humidity conversion is also known. Therefore, to obtain the most accurate humidity
results, both temperature and humidity should be logged.
Temperature compensation uses the following equation:
HTcorr = (Hcorr * K + α*(T-25°C) - β*(T-25°C)²)/(K + γ*(T-25°C)- δ*(T-25°C)²)
Hcorr is the humidity reading with the software correction algorithm for humidity already applied, as explained in
the previous section. The function and values of the other parameters are explained in the table below.
Name
T
K
α
β
Function
Temperature at the time of humidity conversion
Humidity sensor conversion constant
Linear compensation, enumerator
Quadratic compensation, enumerator
γ
Linear compensation, denominator
δ
Quadratic compensation, denominator
Value
(in °C)
0.0307
0.0035/°C
0.000043/°C²
>15°C: 0.00001/°C
≤15°C: -0.00005/°C
0.000002/°C²
Numerical Temperature Compensation Example
Sample Input Data
T = 70°C
Hcorr = 24.445%RH
Application of Correction Coefficients to Sample Reading
γ = 0.00001/°C
HTcorr = (24.445 * 0.0307 + 0.0035 * 45 - 0.000043 * 45²)/ (0.0307
+ 0.00001 * 45 - 0.000002 * 45²)
HTcorr = 30.291 %
SOFTWARE SATURATION DRIFT COMPENSATION
Capacitive humidity sensors read higher humidity values than the actual humidity level when they are exposed to a
high-humidity environment for an extended time period. The DS1923’s humidity sensor produces readings that are
higher than the actual humidity when exposed to humidity levels of about 70%RH and higher. This shift continues
to increase while the device remains at 70%RH and above. This effect is called saturation drift, or sometimes
referred to as hyteresis. This drift is reversible. Readings return to their regular level when the DS1923 is removed
from a high-humidity environment.
It is possible to compensate for most of the error introduced by the saturation drift by post-processing temperature
and humidity logs using the equation below, which is based on laboratory tests and curve-fitting techniques.
Σ
N
HScorr = HTcorr -
-0.3502*k
0.0156 * ARHk * 2.54
1 + (Tk - 25) / 100
k=1
ARHk
The average software corrected and temperature compensated humidity reading of the kth hour that the
device is continuously exposed to 70%RH or higher.
The average software corrected temperature reading of the kth hour that the device is continuously
Tk
exposed to 70%RH or higher.
N
The number of hours that the device is continuously exposed to 70%RH or higher.
HTcorr The humidity reading at the end of the Nth hour with the software correction algorithm for humidity and
temperature compensation already applied. See previous sections for details.
The numbers in the equation are derived from curve fitting. They apply to a time scale in hours.
51 of 53
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Numerical Saturation Drift Compensation Example
Sample Input Data (N = 8)
k (hour)
Tk (°C)
ARHk (%RH)
1
25.1
91.1
2
25.0
92.5
3
24.9
92.9
4
25.0
93.1
5
25.1
93.2
6
25.1
93.3
7
25.0
93.6
8
24.9
93.7
HTcorr = 93.70207 %RH
HScorr
HScorr
=
=
=
Application of Correction Algorithm
Partial Corrections (individual addends)
1.024321
0.751140
0.544824
0.393535
0.283950
0.205086
0.148591
0.107428
Sum of partial corrections:
3.458875
HTcorr - Sum of partial corrections
93.70207 %RH - 3.458875%RH
90.24319%RH
The data in this example was taken from devices that were exposed for several hours to 90%RH at 25°C in a test
chamber. The drift per hour decreases the longer the device is exposed to high humidity. The correction algorithm
compensates for the drift reasonably well. Since the error introduced by the saturation is relatively small, for some
applications compensation may not be necessary.
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DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Revision History
REVISION
DATE
DESCRIPTION
PAGES
CHANGED
Change bullet from “Hydrophobic Filter Protects Sensor Against
Dust, Dirt, Water, and Contaminants” to “Hydrophobic Filter
Protects Sensor Against Dust, Dirt, Contaminants, and Water
Droplets/Condensation”.
Delete “application pending” from UL bullet and safety statement.
120507
Add text to APPLICATION section: Note that the initial sealing
level of DS1923 achieves IP56. Aging and use conditions can
degrade the integrity of the seal over time, so for applications
with significant exposure to liquids, sprays, or other similar
environments, it is recommended to place the Hygrochron under
a shield to protect it (See www.maxim-ic.com/AN4126). The
hydrophobic filter may not protect the DS1923 from destruction in
the event of full submersion in liquid.
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