Dallas DS1982-F3 1-kbit add-only ibutton Datasheet

DS1982
1-kbit Add-Only iButtonTM
www.iButton.com
SPECIAL FEATURES
1024 bits Electrically Programmable ReadOnly Memory (EPROM) communicates with
the economy of one signal plus ground
EPROM partitioned into four 256-bit pages
for randomly accessing packetized data
Each memory page can be permanently
write-protected to prevent tampering
Device is an “add only” memory where
additional data can be programmed into
EPROM without disturbing existing data
Architecture allows software to patch data by
superseding an old page in favor of a newly
programmed page
Reduces control, address, data, power, and
programming signals to a single data pin
8-bit family code specifies DS1982
communications requirements to reader
Reads over a wide voltage range of 2.8V to
6.0V from -40°C to +85°C; programs at
11.5V to 12.0V from -40°C to +50°C
COMMON iButton FEATURES
Unique, factory-lasered and tested 64-bit
registration number (8-bit family code +
48-bit serial number + 8-bit CRC tester)
assures absolute traceability because no two
parts are alike
F3 MICROCAN
Multidrop controller for MicroLAN
Digital identification and information by
momentary contact
Chip-based data carrier compactly stores
information
Data can be accessed while affixed to object
Economically communicates to bus master
with a single digital signal at 16.3 kbits per
second
Standard 16 mm diameter and 1-Wire®
protocol ensure compatibility with iButton
family
Button shape is self-aligning with cupshaped 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 (application pending)
F5 MICROCAN
5.89
3.10
0.36
0.36
0.51
c 1993
0.51
c 1993
16.25
97
09
16.25
YYWW REGISTERED RR
YYWW REGISTERED RR
17
17.35
000000FBC52B
09
17.35
000000FBD8B3
DATA
DATA
GROUND
GROUND
All dimensions shown in millimeters.
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011800
DS1982
ORDERING INFORMATION
EXAMPLES OF ACCESSORIES
DS1982-F3
DS1982-F5
DS9096P
DS9101
DS9093RA
DS9093F
DS9092
F3 MicroCan
F5 MicroCan
Self-Stick Adhesive Pad
Multi-Purpose Clip
Mounting Lock Ring
Snap-In Fob
iButton Probe
iButton DESCRIPTION
The DS1982 1-kbit Add-Only iButton is a rugged read/write data carrier that identifies and stores relevant
information about the product or person to which it is attached. This information can be accessed with
minimal hardware, for example, a single port pin of a microcontroller. The DS1982 consists of a factorylasered registration number that includes an unique 48-bit serial number, an 8–bit CRC, and an 8-bit
Family Code (09h) plus 1 kbit of EPROM which is user-programmable. The power to program and read
the DS1982 is derived entirely from the 1-Wire communication line. Data is transferred serially via the 1Wire protocol which requires only a single data lead and a ground return. The entire device can be
programmed and then write-protected if desired. Alternatively, the part may be programmed multiple
times with new data being appended to, but not overwriting, existing data with each subsequent
programming of the device. Note: Individual bits can be changed only from a logical 1 to a logical 0,
never from a logical 0 to a logical 1. A provision is also included for indicating that a certain page or
pages of data are no longer valid and have been replaced with new or updated data that is now residing at
an alternate page address. This page address redirection allows software to patch data and enhance the
flexibility of the device as a standalone database. The 48-bit serial number that is factory-lasered into
each DS1982 provides a guaranteed unique identity which allows for absolute traceability. The durable
MicroCan package is highly resistant to harsh environments such as dirt, moisture, and shock. Its compact
button-shaped profile is self-aligning with cup-shaped receptacles, allowing the DS1982 to be used easily
by human operators or automatic equipment. Accessories permit the DS1982 to be mounted on printed
circuit boards, plastic key fobs, photo-ID badges, ID bracelets, and many other objects. Applications
include work-in-progress tracking, electronic travelers, access control, storage of calibration constants,
and debit tokens.
OVERVIEW
The block diagram in Figure 1 shows the relationships between the major control and memory sections of
the DS1982. The DS1982 has three main data components: 1) 64-bit lasered ROM, 2) 1024-bit EPROM,
and 3) EPROM Status Bytes. The device derives its power for read operations entirely from the 1-Wire
communication line by storing energy on an internal capacitor during periods of time when the signal line
is high and continues to operate off of this “parasite” power source during the low times of the 1-Wire
line until it returns high to replenish the parasite (capacitor) supply. During programming, 1-Wire
communication occurs at normal voltage levels and then is pulsed momentarily to the programming
voltage to cause the selected EPROM bits to be programmed. The 1-Wire line must be able to provide 12
volts and 10 milliamperes to adequately program the EPROM portions of the part. Whenever
programming voltages are present on the 1-Wire line a special high voltage detect circuit within the
DS1982 generates an internal logic signal to indicate this condition. The hierarchical structure of the 1Wire protocol is shown in Figure 2. The bus master must first provide one of the four ROM function
commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Skip ROM. These commands operate on
the 64-bit lasered ROM portion of each device and can singulate a specific device if many are present on
the 1-Wire line as well as indicate to the bus master how many and what types of devices are present. The
protocol required for these ROM function commands is described in Figure 9. After a ROM function
command is successfully executed, the memory functions that operate on the EPROM portions of the
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DS1982
DS1982 become accessible and the bus master may issue any one of the five memory function commands
specific to the DS1982 to read or program the various data fields. The protocol for these memory function
commands is described in Figure 6. All data is read and written least significant bit first.
64-BIT LASERED ROM
Each DS1982 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 3).
The 64-bit ROM and ROM Function Control section allow the DS1982 to operate as a 1-Wire device and
follow the 1-Wire protocol detailed in the section “1-Wire Bus System.” The memory functions required
to read and program the EPROM sections of the DS1982 are not accessible until the ROM function
protocol has been satisfied. This protocol is described in the ROM functions flow chart (Figure 9). The 1Wire bus master must first provide one of four ROM function commands: 1) Read ROM, 2) Match ROM,
3) Search ROM, or 4) Skip ROM. After a ROM function sequence has been successfully executed, the
bus master may then provide any one of the memory function commands specific to the DS1982 (Figure
6).
The 1-Wire CRC of the lasered ROM is generated using the polynomial X8 + X5 + X4 + 1. Additional
information about the Dallas Semiconductor 1-Wire Cyclic Redundancy Check is available in the Book
of DS19xx iButton Standards. The shift register acting as the CRC accumulator is initialized to 0. Then
starting with the least significant bit of the family code, 1 bit at a time is shifted in. After the 8th bit of the
family code has been entered, then the serial number is entered. After the 48th bit of the serial number has
been entered, the shift register contains the CRC value. Shifting in the 8 bits of CRC should return the
shift register to all 0s.
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DS1982
DS1982 BLOCK DIAGRAM Figure 1
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DS1982
HIERARCHICAL STRUCTURE FOR 1-WIRE PROTOCOL Figure 2
OTHER
DEVICES
BUS
MASTER
DS 1982
COMMAND
LEVEL:
1-WIRE ROM FUNCTION
COMMANDS (SEE FIGURE 9)
DS1982-SPECIFIC
MEMORY FUNCTION
COMMANDS
(SEE FIGURE 6)
AVAILABLE
COMMANDS:
DATA FIELD
AFFECTED:
READ ROM
MATCH ROM
SEARCH ROM
SKIP ROM
64-BIT ROM
64-BIT ROM
64-BIT ROM
N/A
WRITE MEMORY
WRITE STATUS BYTE
READ MEMORY
READ STATUS BYTE
READ DATA/GENERATE
8-BIT CRC
1024-BIT EPROM
EPROM STATUS BYTES
1024-BIT EPROM
EPROM STATUS BYTES
1024-BIT EPROM
64-BIT LASERED ROM Figure 3
8-Bit CRC Code
MSB
48- Bit Serial Number
LSB MSB
8- Bit Family Code (09h)
LSB MSB
1-WIRE CRC GENERATOR Figure 4
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LSB
DS1982
1024-BIT EPROM
The memory map in Figure 5 shows the 1024-bit EPROM section of the DS1982 which is configured as
four pages of 32 bytes each. The 8-bit scratchpad is an additional register that acts as a buffer when
programming the memory. Data is first written to the scratchpad and then verified by reading an 8-bit
CRC from the DS1982 that confirms proper receipt of the data. If the buffer contents are correct, a
programming voltage should be applied and the byte of data will be written into the selected address in
memory. This process ensures data integrity when programming the memory. The details for reading and
programming the 1024-bit EPROM portion of the DS1982 are given in the "Memory Function
Commands" section.
EPROM STATUS BYTES
In addition to the 1024 bits of data memory the DS1982 provides 64 bits of status memory accessible
with separate commands.
The EPROM Status Bytes can be read or programmed to indicate various conditions to the software
interrogating the DS1982. The first byte of the EPROM status memory contains the Write-Protect Page
bits which inhibit programming of the corresponding page in the 1024-bit main memory area if the
appropriate write protection bit is programmed. Once a bit has been programmed in the Write-Protect
Page byte, the entire 32-byte page that corresponds to that bit can no longer be altered but may still be
read.
The next 4 bytes of the EPROM Status Memory contain the Page Address Redirection Bytes which
indicate if one or more of the pages of data in the 1024-bit EPROM section have been invalidated and
redirected to the page address contained in the appropriate redirection byte. The hardware of the DS1982
makes no decisions based on the contents of the Page Address Redirection Bytes. These additional bytes
of status EPROM allow for the redirection of an entire page to another page address, indicating that the
data in the original page is no longer considered relevant or valid. With EPROM technology, bits within a
page can be changed from a logical 1 to a logical 0 by programming, but cannot be changed back.
Therefore, it is not possible to simply rewrite a page if the data requires changing or updating, but with
space permitting, an entire page of data can be redirected to another page within the DS1982 by writing
the one’s complement of the new page address into the Page Address Redirection Byte that corresponds
to the original (replaced) page.
This architecture allows the user’s software to make a “data patch” to the EPROM by indicating that a
particular page or pages should be replaced with those indicated in the Page Address Redirection Bytes.
If a Page Address Redirection Byte has a FFH value, the data in the main memory that corresponds to that
page is valid. If a Page Address Redirection Byte has some other hex value, the data in the page
corresponding to that redirection byte is invalid, and the valid data can now be found at the one’s
complement of the page address indicated by the hex value stored in the associated Page Address
Redirection Byte. A value of FDH in the redirection byte for page 1, for example, would indicate that the
updated data is now in page 2. The details for reading and programming the EPROM status memory
portion of the DS1982 is given in the Memory Function Commands section.
MEMORY FUNCTION COMMANDS
The “Memory Function Flow Chart” (Figure 6) describes the protocols necessary for accessing the
various data fields within the DS1982. The Memory Function Control section, 8-bit scratchpad, and the
Program Voltage Detect circuit combine to interpret the commands issued by the bus master and create
the correct control signals within the device. A 3-byte protocol is issued by the bus master. It is comprised
of a command byte to determine the type of operation and 2 address bytes to determine the specific
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DS1982
starting byte location within a data field. The command byte indicates if the device is to be read or
written. Writing data involves not only issuing the correct command sequence but also providing a 12volt programming voltage at the appropriate times. To execute a write sequence, a byte of data is first
loaded into the scratchpad and then programmed into the selected address. Write sequences always occur
a byte at a time. To execute a read sequence, the starting address is issued by the bus master and data is
read from the part beginning at that initial location and continuing to the end of the selected data field or
until a reset sequence is issued. All bits transferred to the DS1982 and received back by the bus master
are sent least significant bit first.
DS1982 MEMORY MAP Figure 5
8-BIT SCRATCHPAD
STARTING
ADDRESS
0000h
1024-BIT
EPROM
PAGE 0
32 BYTES
0020h
PAGE 1
32 BYTES
0040h
PAGE 2
32 BYTES
0060h
PAGE 3
32 BYTES
EPROM STATUS BYTES
ADDRESS:
0007h
(MSB)
0006h
0005h
BIT 0
BIT 1
BIT 2
BIT 3
BIT 4-7
0004h
0003h
0002h
0001h
0000h
(LSB)
WRITE PROTECT PAGE 0
WRITE PROTECT PAGE 1
WRITE PROTECT PAGE 2
WRITE PROTECT PAGE 3
BITMAP OF USED PAGES (RESERVED FOR TMEX)
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DS1982
MEMORY FUNCTION FLOW CHART Figure 6
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DS1982
MEMORY FUNCTION FLOW CHART (cont’d) Figure 6
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DS1982
MEMORY FUNCTION FLOW CHART (cont’d) Figure 6
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DS1982
READ MEMORY [F0h]
The Read Memory command is used to read data from the 1024-bit EPROM data field. The bus master
follows the command byte with a 2-byte address (TA1=(T7:T0), TA2=(T15:T8)) that indicates a starting
byte location within the data field. An 8–bit CRC of the command byte and address bytes is computed by
the DS1982 and read back by the bus master to confirm that the correct command word and starting
address were received. If the CRC read by the bus master is incorrect, a Reset Pulse must be issued and
the entire sequence must be repeated. If the CRC received by the bus master is correct, the bus master
issues read time slots and receives data from the DS1982 starting at the initial address and continuing
until the end of the 1024-bit data field is reached or until a Reset Pulse is issued. If reading occurs
through the end of memory space, the bus master may issue eight additional read time slots and the
DS1982 will respond with an 8-bit CRC of all data bytes read from the initial starting byte through the
last byte of memory. After the CRC is received by the bus master, any subsequent read time slots will
appear as logical 1s until a Reset Pulse is issued. Any reads ended by a Reset Pulse prior to reaching the
end of memory will not have the 8-bit CRC available.
Typically a 16-bit CRC would be stored with each page of data to ensure rapid, error-free data transfers
that eliminate having to read a page multiple times to determine if the received data is correct or not. (See
Book of DS19xx iButton Standards, Chapter 7 for the recommended file structure to be used with the 1Wire environment.) If CRC values are imbedded within the data, a Reset Pulse may be issued at the end
of memory space during a Read Memory command.
READ STATUS [AAh]
The Read Status command is used to read data from the EPROM Status data field. The bus master
follows the command byte with a two byte address (TA1=(T7:T0), TA2=(T15:T8)) that indicates a
starting byte location within the data field. An 8–bit CRC of the command byte and address bytes is
computed by the DS1982 and read back by the bus master to confirm that the correct command word and
starting address were received. If the CRC read by the bus master is incorrect, a Reset Pulse must be
issued and the entire sequence must be repeated. If the CRC received by the bus master is correct, the bus
master issues read time slots and receives data from the DS1982 starting at the supplied address and
continuing until the end of the EPROM Status data field is reached. At that point the bus master will
receive an 8-bit CRC that is the result of shifting into the CRC generator all of the data bytes from the
initial starting byte through the final factory-programmed byte that contains the 00h value.
This feature is provided since the EPROM Status information may change over time making it impossible
to program the data once and include an accompanying CRC that will always be valid. Therefore, the
Read Status command supplies an 8-bit CRC that is based on and always is consistent with the current
data stored in the EPROM Status data field.
After the 8-bit CRC is read, the bus master will receive logical 1s from the DS1982 until a Reset Pulse is
issued. The Read Status command sequence can be exited at any point by issuing a Reset Pulse.
READ DATA/GENERATE 8-BIT CRC [C3h]
The Read Data/Generate 8-bit CRC command is used to read data from the 1024-bit EPROM memory
field. The bus master follows the command byte with a two byte address (TA1=(T7:T0), TA2=(T15:T8))
that indicates a starting byte location within the data field. An 8-bit CRC of the command byte and
address bytes is computed by the DS1982 and read back by the bus master to confirm that the correct
command word and starting address were received. If the CRC read by the bus master is incorrect, a
Reset Pulse must be issued and the entire sequence must be repeated. If the CRC received by the bus
master is correct, the bus master issues read time slots and receives data from the DS1982 starting at the
initial address and continuing until the end of a 32-byte page is reached. At that point the bus master will
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DS1982
send eight additional read time slots and receive an 8-bit CRC that is the result of shifting into the CRC
generator all of the data bytes from the initial starting byte to the last byte of the current page. Once the
8-bit CRC has been received, data is again read from the 1024-bit EPROM data field starting at the next
page. This sequence will continue until the final page and its accompanying CRC are read by the bus
master. Thus each page of data can be considered to be 33 bytes long, the 32 bytes of user-programmed
EPROM data and an 8-bit CRC that gets generated automatically at the end of each page.
This type of read differs from the Read Memory command which simply reads each page until the end of
address space is reached. The Read Memory command only generates an 8-bit CRC at the end of memory
space that often might be ignored, since in many applications the user would store a 16-bit CRC with the
data itself in each page of the 1024-bit EPROM data field at the time the page was programmed. The
Read Data/Generate 8-bit CRC command provides an alternate read capability for applications that are
“bit-oriented” rather than “page-oriented” where the 1024-bit EPROM information may change over time
within a page boundary, making it impossible to program the page once and include an accompanying
CRC that will always be valid. Therefore, the Read Data/Generate 8-Bit CRC command concludes each
page with the DS1982 generating and supplying an 8-bit CRC that is based on and therefore is always
consistent with the current data stored in each page of the 1024-bit EPROM data field. After the 8-bit
CRC of the last page is read, the bus master will receive logical 1s from the DS1982 until a Reset Pulse is
issued. The Read Data/Generate 8-Bit CRC command sequence can be exited at any point by issuing a
Reset Pulse.
WRITE MEMORY [0Fh]
The Write Memory command is used to program the 1024–bit EPROM data field. The bus master will
follow the command byte with a two byte starting address (TA1=(T7:T0), TA2=(T15:T8)) and a byte of
data (D7:D0). An 8-bit CRC of the command byte, address bytes, and data byte is computed by the
DS1982 and read back by the bus master to confirm that the correct command word, starting address, and
data byte were received.
The highest starting address within the DS1982 is 007FH. If the bus master sends a starting address
higher than this, the nine most significant address bits are set to 0 by the internal circuitry of the chip.
This will result in a mismatch between the CRC calculated by the DS1982 and the CRC calculated by the
bus master, indicating an error condition.
If the CRC read by the bus master is incorrect, a Reset Pulse must be issued and the entire sequence must
be repeated. If the CRC received by the bus master is correct, a programming pulse (12 volts on the 1Wire bus for 480 µs) is issued by the bus master. Prior to programming, the entire unprogrammed
1024-bit EPROM data field will appear as logical 1s. For each bit in the data byte provided by the bus
master that is set to a logical 0, the corresponding bit in the selected byte of the 1024–bit EPROM will be
programmed to a logical 0 after the programming pulse has been applied at that byte location.
After the 480 µs programming pulse is applied and the data line returns to a 5-volt level, the bus master
issues eight read time slots to verify that the appropriate bits have been programmed. The DS1982
responds with the data from the selected EPROM address sent least significant bit first. This byte contains
the logical AND of all bytes written to this EPROM data address. If the EPROM data byte contains 1s in
bit positions where the byte issued by the master contains 0s, a Reset Pulse should be issued and the
current byte address should be programmed again. If the DS1982 EPROM data byte contains 0s in the
same bit positions as the data byte, the programming was successful and the DS1982 will automatically
increment its address counter to select the next byte in the 1024-bit EPROM data field. The least
significant byte of the new 2-byte address will also be loaded into the 8-bit CRC generator as a starting
value. The bus master will issue the next byte of data using eight write time slots.
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DS1982
As the DS1982 receives this byte of data into the scratchpad, it also shifts the data into the CRC generator
that has been preloaded with the LSB of the current address, and the result is an 8-bit CRC of the new
data byte and the LSB of the new address. After supplying the data byte, the bus master will read this
8-bit CRC from the DS1982 with eight read time slots to confirm that the address incremented properly
and the data byte was received correctly. If the CRC is incorrect, a Reset Pulse must be issued and the
Write Memory command sequence must be restarted. If the CRC is correct, the bus master will issue a
programming pulse and the selected byte in memory will be programmed.
Note that the initial pass through the Write Memory flow chart will generate an 8-bit CRC value that is
the result of shifting the command byte into the CRC generator, followed by the 2 address bytes, and
finally the data byte. Subsequent passes through the Write Memory flow chart due to the DS1982
automatically incrementing its address counter will generate an 8-bit CRC that is the result of loading (not
shifting) the LSB of the new (incremented) address into the CRC generator and then shifting in the new
data byte.
For both of these cases, the decision to continue (to apply a program pulse to the DS1982) is made
entirely by the bus master, since the DS1982 will not be able to determine if the 8-bit CRC calculated by
the bus master agrees with the 8-bit CRC calculated by the DS1982. If an incorrect CRC is ignored and a
program pulse is applied by the bus master, incorrect programming could occur within the DS1982. Also
note that the DS1982 will always increment its internal address counter after the receipt of the eight read
time slots used to confirm the programming of the selected EPROM byte. The decision to continue is
again made entirely by the bus master; therefore if the EPROM data byte does not match the supplied
data byte but the master continues with the Write Memory command, incorrect programming could occur
within the DS1982. The Write Memory command sequence can be exited at any point by issuing a Reset
Pulse.
WRITE STATUS [55h]
The Write Status command is used to program the EPROM Status data field. The bus master will follow
the command byte with a 2-byte starting address (TA1=(T7:T0), TA2=(T15:T8)) and a byte of status data
(D7:D0). An 8-bit CRC of the command byte, address bytes, and data byte is computed by the DS1982
and read back by the bus master to confirm that the correct command word, starting address, and data
byte were received.
If the CRC read by the bus master is incorrect, a Reset Pulse must be issued and the entire sequence must
be repeated. If the CRC received by the bus master is correct, a programming pulse (12 volts on the 1Wire bus for 480 µs) is issued by the bus master. Prior to programming, the first 7 bytes of the EPROM
Status data field will appear as logical 1s. For each bit in the data byte provided by the bus master that is
set to a logical 0, the corresponding bit in the selected byte of the EPROM Status data field will be
programmed to a logical 0 after the programming pulse has been applied at that byte location. The 8th
byte of the EPROM status byte data field is factory-programmed to contain 00h.
After the 480 µs programming pulse is applied and the data line returns to a 5-volt level, the bus master
issues eight read time slots to verify that the appropriate bits have been programmed. The DS1982
responds with the data from the selected EPROM Status address sent least significant bit first. This byte
contains the logical AND of all bytes written to this EPROM Status Byte address. If the EPROM Status
Byte contains 1s in bit positions where the byte issued by the master contained 0s, a Reset Pulse should
be issued and the current byte address should be programmed again. If the DS1982 EPROM Status Byte
contains 0s in the same bit positions as the data byte, the programming was successful and the DS1982
will automatically increment its address counter to select the next byte in the EPROM Status data field.
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DS1982
The least significant byte of the new 2-byte address will also be loaded into the 8-bit CRC generator as a
starting value. The bus master will issue the next byte of data using eight write time slots.
As the DS1982 receives this byte of data into the scratchpad, it also shifts the data into the CRC generator
that has been preloaded with the LSB of the current address and the result is an 8-bit CRC of the new data
byte and the LSB of the new address. After supplying the data byte, the bus master will read this 8-bit
CRC from the DS1982 with eight read time slots to confirm that the address incremented properly and the
data byte was received correctly. If the CRC is incorrect, a Reset Pulse must be issued and the Write
Status command sequence must be restarted. If the CRC is correct, the bus master will issue a
programming pulse and the selected byte in memory will be programmed.
Note that the initial pass through the Write Status flow chart will generate an 8-bit CRC value that is the
result of shifting the command byte into the CRC generator, followed by the 2 address bytes, and finally
the data byte. Subsequent passes through the Write Status flow chart due to the DS1982 automatically
incrementing its address counter will generate an 8-bit CRC that is the result of loading (not shifting) the
LSB of the new (incremented) address into the CRC generator and then shifting in the new data byte.
For both of these cases, the decision to continue (to apply a program pulse to the DS1982) is made
entirely by the bus master, since the DS1982 will not be able to determine if the 8-bit CRC calculated by
the bus master agrees with the 8-bit CRC calculated by the DS1982. If an incorrect CRC is ignored and a
program pulse is applied by the bus master, incorrect programming could occur within the DS1982. Also
note that the DS1982 will always increment its internal address counter after the receipt of the eight read
time slots used to confirm the programming of the selected EPROM byte. The decision to continue is
again made entirely by the bus master, therefore if the EPROM data byte does not match the supplied
data byte but the master continues with the Write Status command, incorrect programming could occur
within the DS1982. The Write Status command sequence can be ended at any point by issuing a Reset
Pulse.
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
DS1982 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 type and timing). A 1-Wire protocol defines bus transactions in terms of the bus state
during specified 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 an
open drain connection or 3-state outputs. The DS1982 is an open drain part with an internal circuit
equivalent to that shown in Figure 7. The bus master can be the same equivalent circuit. If a bidirectional
pin is not available, separate output and input pins can be tied together.
The bus master requires a pullup resistor at the master end of the bus, with the bus master circuit
equivalent to the one shown in Figures 8a and 8b. The value of the pullup resistor should be
approximately 5 kΩ=for short line lengths.
A multidrop bus consists of a 1-Wire bus with multiple slaves attached. The 1-Wire bus has a maximum
data rate of 16.3 kbits per second. If the bus master is also required to perform programming of the
EPROM portions of the DS1982, a programming supply capable of delivering up to 10 milliamps at 12
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DS1982
volts for 480 µs is required. 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 120 µs, one or more of the devices on the bus may be
reset.
TRANSACTION SEQUENCE
The sequence for accessing the DS1982 via the 1-Wire port is as follows:
Initialization
ROM Function Command
Memory Function Command
Read/Write Memory/Status
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 a presence pulse(s) transmitted by the
slave(s).
The presence pulse lets the bus master know that the DS1982 is on the bus and is ready to operate. For
more details, see the “1-Wire Signaling” section.
ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the four ROM function commands. All
ROM function commands are 8 bits long. A list of these commands follows (refer to flowchart in Figure
9):
Read ROM [33h]
This command allows the bus master to read the DS1982’s 8-bit family code, unique 48-bit serial
number, and 8-bit CRC. This command can be used only if there is a single DS1982 on the bus. If more
than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same
time (open drain will produce a wired-AND result).
Match ROM [55h]
The match ROM command, followed by a 64–bit ROM sequence, allows the bus master to address a
specific DS1982 on a multidrop bus. Only the DS1982 that exactly matches the 64-bit ROM sequence
will respond to the subsequent memory function command. All slaves that do not match the 64-bit ROM
sequence will wait for a Reset Pulse. This command can be used with a single or multiple devices on the
bus.
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DS1982
DS1982 EQUIVALENT CIRCUIT Figure 7
BUS MASTER CIRCUIT Figure 8
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DS1982
ROM FUNCTIONS FLOW CHART Figure 9
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DS1982
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 a read command is issued following the Skip ROM command, data collision will occur on the bus as
multiple slaves transmit simultaneously (open drain pull–downs will produce a wired-AND result).
Search ROM [F0h]
When a system is initially brought up, the bus master might not know the number of devices on the 1Wire bus or their 64-bit ROM codes. The search ROM command allows the bus master to use a process
of elimination to identify the 64-bit ROM codes of all slave devices on the bus. The ROM search process
is the repetition of a simple, three-step routine: read a bit, read the complement of the bit, then write the
desired value of that bit. The bus master performs this simple, three-step routine on each bit of the ROM.
After one complete pass, the bus master knows the contents of the ROM in one device. The remaining
number of devices and their ROM codes may be identified by additional passes. See Chapter 5 of the
Book of DS19xx iButton Standards for a comprehensive discussion of a ROM search, including an actual
example.
1-Wire Signaling
The DS1982 requires strict protocols to ensure data integrity. The protocol consists of five types of
signaling on one line: Reset Sequence with Reset Pulse and Presence Pulse, Write 0, Write 1, Read Data
and Program Pulse. All these signals except presence pulse are initiated by the bus master. The
initialization sequence required to begin any communication with the DS1982 is shown in Figure 10. A
Reset Pulse followed by a presence pulse indicates the DS1982 is ready to accept a ROM command. The
bus master transmits (TX) a Reset Pulse (tRSTL , minimum 480 µs). The bus master then releases the line
and goes into receive mode (RX). The 1-Wire bus is pulled to a high state via the pullup resistor. After
detecting the rising edge on the 1-Wire line, the DS1982 waits (tPDH , 15-60 µs) and then transmits the
presence pulse (tPDL , 60-240 µs).
Read/Write Time Slots
The definitions of write and read time slots are illustrated in Figure 11. All time slots are initiated by the
master driving the data line low. The falling edge of the data line synchronizes the DS1982 to the master
by triggering a delay circuit in the DS1982. During write time slots, the delay circuit determines when the
DS1982 will sample the data line. For a read data time slot, if a 0 is to be transmitted, the delay circuit
determines how long the DS1982 will hold the data line low overriding the 1 generated by the master. If
the data bit is a 1, the device will leave the read data time slot unchanged.
PROGRAM PULSE
To copy data from the 8-bit scratchpad to the EPROM Data or Status Memory, a program pulse of 12
volts is applied to the data line after the bus master has confirmed that the CRC for the current byte is
correct. During programming, the bus master controls the transition from a state where the data line is
idling high via the pullup resistor to a state where the data line is actively driven to a programming
voltage of 12 volts providing a minimum of 10 mA of current to the DS1982. This programming voltage
(Figure 12) should be applied for 480 µs, after which the bus master returns the data line to an idle high
state controlled by the pullup resistor. Note that due to the high voltage programming requirements for
any 1-Wire EPROM device, it is not possible to multidrop non-EPROM based 1-Wire devices with the
DS1982 during programming. An internal diode within the non-EPROM based 1-Wire devices will
attempt to clamp the data line at approximately 8 volts and could potentially damage these devices.
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DS1982
CRC GENERATION
The DS1982 has an 8-bit CRC 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 DS1982 to determine if the ROM data has been received error-free by the bus master. The equivalent
polynomial function of this CRC is: X8 + X5 + X4 + 1.
Under certain conditions, the DS1982 also generates an 8-bit CRC value using the same polynomial
function shown above and provides this value to the bus master to validate the transfer of command,
address, and data bytes from the bus master to the DS1982. The Memory Function Flow Chart of Figure
6 indicates that the DS1982 computes an 8-bit CRC for the command, address, and data bytes received
for the Write Memory and the Write Status commands and then outputs this value to the bus master to
confirm proper transfer. Similarly the DS1982 computes an 8–bit CRC for the command and address
bytes received from the bus master for the Read Memory, Read Status, and Read Data/Generate 8-Bit
CRC commands to confirm that these bytes have been received correctly. The CRC generator on the
DS1982 is also used to provide verification of error-free data transfer as each page of data from the 1024bit EPROM is sent to the bus master during a Read Data/Generate 8-bit CRC command, and for the 8
bytes of information in the status memory field.
In each case where a CRC is used for data transfer validation, the bus master must calculate a CRC value
using the polynomial function given above and compare the calculated value to either the 8-bit CRC
value stored in the 64-bit ROM portion of the DS1982 (for ROM reads) or the 8-bit CRC value computed
within the DS1982. The comparison of CRC values and decision to continue with an operation are
determined entirely by the bus master. There is no circuitry on the DS1982 that prevents a command
sequence from proceeding if the CRC stored in or calculated by the DS1982 does not match the value
generated by the bus master. Proper use of the CRC as outlined in the flow chart of Figure 6 can result in
a communication channel with a very high level of integrity. For more details on generating CRC values
including example implementations in both hardware and software, see the Book of DS19xx iButton
Standards.
INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 10
MASTER TX "RESET PULSE"
RESISTOR
MASTER
DS1982
MASTER RX "RESET PULSE"
480 µs ≤ tRSTL < *
480 µs ≤ tRSTH < ∞ (includes recovery time)
15 µs ≤ tPDH < 60 µs
60 µs ≤ tPDL < 240 µs
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DS1982
∗
In order not to mask interrupt signaling by other devices on the 1-Wire bus, tRSTL + tR should always
be less than 960 µs.
READ/WRITE TIMING DIAGRAM Figure 11
Write-1 Time Slot
60 µs ≤ tSLOT < 120 µs
1 µs ≤ tLOW1 < 15 µs
1 µs ≤ tREC < ∞
Write-0 Time Slot
RESISTOR
60 µs ≤ tLOW0 < tSLOT < 120 µs
1 µs ≤ tREC < ∞
MASTER
DS1982
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DS1982
Read-data Time Slot
RESISTOR
MASTER
DS1982
60 µs ≤ tSLOT < 120 µs
1 µs ≤ tLOWR < 15 µs
0 ≤ tRELEASE < 45 µs
1 µs ≤ tREC < ∞
tRDV = 15 µs
tSU < 1 µs
PROGRAM PULSE TIMING DIAGRAM Figure 12
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DS1982
ABSOLUTE MAXIMUM RATINGS*
Voltage on any Pin Relative to Ground
Operating Temperature
Storage Temperature
∗
–0.5V to +12.0V
–40°C to +85°C
–55°C to +125°C
This is a stress rating only and functional operation of the device at these or any other conditions
outside 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.
DC ELECTRICAL CHARACTERISTICS
PARAMETER
Logic 1
Logic 0
Output Logic Low @ 4 mA
Output Logic High
Input Load Current
Operating Charge
Programming Voltage @ 10 mA
SYMBOL
VIH
VIL
VOL
VOH
IL
QOP
VPP
(VPUP=2.8V to 6.0V; -40°C to +85°C)
MIN
2.2
-0.3
TYP
VPUP
5
MAX
+0.8
0.4
6.0
30
12.0
11.5
CAPACITANCE
PARAMETER
Data (1-Wire)
NOTES
1, 6
1, 11
1
1, 2
3
7, 8
(T A = 25°C)
SYMBOL
CIN/OUT
MIN
AC ELECTRICAL CHARACTERISTICS
PARAMETER
Time Slot
Write 1 Low Time
Write 0 Low Time
Read Data Valid
Release Time
Read Data Setup
Recovery Time
Reset Time High
Reset Time Low
Presence Detect High
Presence Detect Low
Delay to Program
Delay to Verify
Program Pulse Width
Program Voltage Rise Time
Program Voltage Fall Time
UNITS
V
V
V
V
µA
nC
V
SYMBOL
tSLOT
tLOW1
tLOW0
tRDV
tRELEASE
tSU
tREC
tRSTH
tRSTL
tPDHIGH
tPDLOW
tDP
tDV
tPP
tRP
tFP
TYP
MAX
800
UNITS
pF
NOTES
9
(VPUP=2.8V to 6.0V; -40°C to +85°C)
MIN
60
1
60
0
1
480
480
15
60
5
5
480
0.5
0.5
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TYP
MAX
120
15
120
exactly 15
15
45
1
60
240
5000
5.0
5.0
UNITS
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
µs
NOTES
5
4
10
10
10,12
10
10
DS1982
NOTES:
1. All voltages are referenced to ground.
2. VPUP = external pullup voltage.
3. Input load is to ground.
4. An additional reset or communication sequence cannot begin until the reset high time has expired.
5. Read data setup time refers to the time the host must pull the 1-Wire bus low to read a bit. Data is
guaranteed to be valid within 1 µs of this falling edge and will remain valid for 14 µs minimum. (15
µs total from falling edge on 1-Wire bus.)
6. VIH is a function of the external pullup resistor and the pullup voltage.
7. 30 nanocoulombs per 72 time slots @ 5.0V.
8. At VCC =5.0V with a 5 kΩ pullup to VCC and a maximum time slot of 120 µs.
9. Capacitance on the data pin could be 800 pF when power is first applied. If a 5 kΩ resistor is used to
pull up the data line to VCC , 5 ms after power has been applied the parasite capacitance will not affect
normal communications.
10. Maximum 1-Wire voltage for programming parameters is 11.5V to 12.0V; temperature range is -40°C
to +50°C.
11. Under certain low voltage conditions VILMAX may have to be reduced to as much as 0.5V to always
guarantee a presence pulse.
12. The accumulative duration of the programming pulses for each address must not exceed 5 ms.
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