Dallas DS2480BS Serial 1-wire line driver with load sensor Datasheet

DS2480B
Serial 1-WireTM Line
Driver with Load Sensor
www.dalsemi.com
FEATURES
PIN ASSIGNMENT
§ Universal, common-ground serial port to 1Wire line driver for MicroLAN applications
§ Works with all iButtons and MicroLANcompatible 1-Wire slave devices
§ Communicates at regular and Overdrive 1Wire speed and serial port data rates of 9600
(default), 19200, 57600 and 115200 bps
§ Supports 12V EPROM programming and stiff
5V pullup for crypto iButton, sensors and
EEPROM
§ Load sensor to terminate the stiff pullup as
the energy demand of the crypto iButton
drops
§ Self-calibrating time base with ± 5%
tolerance for serial and 1-Wire
communication
§ Slew rate controlled 1-Wire pulldown and
active pullup to accommodate long lines and
reduce radiation
§ User-selectable RXD/TXD polarity
minimizes component count when interfacing
to 5V based RS232 systems or directly to
UARTs
§ Programmable 1-Wire timing and driver
characteristics accommodate a wide range of
MicroLAN configurations at regular speed
§ Smart protocol combines data and control
information without requiring extra pins
§ Compatible with optical, IR and RF to RS232
converters
§ Low cost 8-pin SOIC surface mount package
§ Operates over 4.5V to 5.5V from -40°C to
+85°C
GND
1
8
RXD
1-W
2
7
TXD
NC
3
6
POL
VDD
4
5
VPP
8-Pin SOIC (150-mil)
PIN DESCRIPTION
GND
1-W
NC
VDD
VPP
POL
TXD
RXD
- Ground
- 1-Wire Input/Output
- No Connection
- 4.5 to 5.5 Volts
- Optional EPROM
Programming Voltage
- RXD/TXD Polarity Select
- Serial Data from UART
- Serial Data to UART
ORDERING INFORMATION
DS2480BS
8-pin SOIC
Note: The DS2480B will replace the DS2480
later in 1999. It is fully backward compatible to
software drivers that accept a 0 as well as a 1 for
bit 2 of the Reset-command response byte (see
page 7, Table 2)
DESCRIPTION
The DS2480B is a serial port to 1-Wire interface chip that supports regular and Overdrive speeds. It connects directly to UARTs and 5V RS232 systems. Interfacing to RS232C (± 12V levels) requires a passive
clamping circuit and one 5V to ±12V level translator. Internal timers relieve the host of the burden of
generating the time-critical 1-Wire communication waveforms. In contrast to the DS9097(E) where a full
character must be sent by the host for each 1-Wire time slot, the DS2480B can translate each character
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into eight 1-Wire time slots, thereby increasing the data throughput significantly. In addition, the
DS2480B can be set to communicate at four different data rates, including 115.2 kbps, 57.6 kbps and 19.2
kbps with 9.6 kbps being the power-on default. Command codes received from the host’s crystal
controlled UART serve as a reference to continuously calibrate the on-chip timing generator. The
DS2480B uses a unique protocol that merges data and control information without requiring control pins.
This approach maintains compatibility to off-the-shelf serial to wireless converters, allowing easy
realization of 1-Wire media jumpers. The various control functions of the DS2480B are optimized for
MicroLAN 1-Wire networks and support the special needs of all current 1-Wire devices including the
crypto iButton, EPROM-based Add-Only Memories, EEPROM devices and 1-Wire Thermometers.
DETAILED PIN DESCRIPTION
PIN
1
2
SYMBOL
GND
1-W
3
4
NC
VDD
5
VPP
6
POL
7
TXD
8
RXD
DESCRIPTION
Ground Pin: common ground reference and ground return for 1-Wire bus
1–Wire Input/Output Pin: 1–Wire bus with slew–rate–controlled pulldown,
active pullup, ability to switch in VPP to program EPROM, and ability to switch
in VDD through a low–impedance path to program EEPROM, perform a
temperature conversion or operate the crypto iButton.
No Connection Pin.
Power Input Pin: power supply for the chip and 1–Wire pullup voltage, 5V
±10%, must always be lower than VPP. VDD should be derived from VPP by a
separate voltage regulator. If EPROM programming is not required feed VDD
from VPP through a Schottky diode to get a 0.3V drop at VDD.
EPROM Programming Voltage: 12V supply input for EPROM programming.
If EPROM programming is not required, connect this pin directly to the system’s
5V supply.
RXD/TXD Polarity Select: RXD/TXD polarity select; tied to GND for RS232
(12V or 5V) connection; tied to VDD for direct connection to UART chip.
Serial Data from UART: data input from host (inverted or true); maximum
voltage swing –0.3V to VDD + 0.3V; for logic thresholds see DC specifications.
Serial Data to UART: signal output to host; push–pull driver with CMOS
compatible levels; for true ±12V RS232 systems an external level translator must
be provided.
OVERVIEW
The DS2480B directly interfaces a 5V serial communication port with its lines TXD (transmit) and RXD
(receive) to a 1–Wire bus. In addition the device performs a speed conversion allowing the data rate at the
communication port to be different from the 1–Wire data rate. Several parameters relating to the 1–Wire
port and its timing as well as the communication speed at both the port and the 1–Wire bus are
configurable. The circuit to achieve these functions is outlined in Figure 1, Block Diagram.
The device gets its input data from the serial communication port of the host computer through pin TXD.
For compatibility with active–high as well as active–low systems, the incoming signal can be inverted by
means of the polarity input POL. The polarity chosen by hard–wiring the logic level of this pin is also
valid for the output pin RXD. If for minimizing the interface hardware an asymmetry between RXD and
TXD is desired, this can be achieved by setting the most significant bit of the Speed Control parameter to
a 1 (see Configuration Parameter Value Codes). With the MS bit of the speed control set to 1, the polarity
at TXD is still selected by the logic level at POL, but the polarity at RXD will be the opposite of what the
logic level at POL specifies.
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As data enters the core of the DS2480B’s logic circuitry, it is analyzed to separate data and command
bytes and to calibrate the device’s timing generator. The timing generator controls all speed relations of
the communication interface and the 1–Wire bus as well as the wave forms on the 1–Wire bus.
Command bytes either affect the configuration setting or generate certain wave forms on the 1–Wire bus.
Data bytes are simply translated by the protocol converter into the appropriate 1–Wire activities. Each
data byte generates a return byte from the 1–Wire bus that is communicated back to the host through the
RXD pin as soon as the activity on the 1–Wire bus is completed.
The 1–Wire driver shapes the slopes of the 1–Wire wave forms, applies programming pulses or strong
pullup to 5 volts and reads the 1–Wire bus using a non–TTL threshold to maximize the noise margin for
best performance on large 1–Wire MicroLAN networks.
DS2480B BLOCK DIAGRAM Figure 1
DEVICE OPERATION
The DS2480B can be described as a complex state machine with two static and several dynamic states.
Two device–internal flags as well as functions assigned to certain bit positions in the command codes
determine the behavior of the chip, as shown in the state transition diagram (Figure 2). The DS2480B
requires and generates a communication protocol of 8 data bits per character, 1 stop bit and no parity. It is
permissible to use 2 stop bits on the TXD line. However, the DS2480B will only assert a single stop bit
on RXD.
When powering up, the DS2480B performs a master reset cycle and enters the Command Mode, which
is one of the two static states. The device now expects to receive one 1–Wire reset command on the TXD
line sent by the host at a data rate of 9600 bits per second (see section Communication Commands for
details). This command byte is required solely for calibration of the timing generator the DS2480B and is
not translated into any activity on the 1–Wire bus. After this first command byte the device is ready to
receive and execute any command as described later in this document.
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STATE TRANSITION DIAGRAM Figure 2
LEGEND:
V
SS
P
T
Q
H
ZZZ
VVV
X
BINARY VALUE (TYPE OF WRITE TIME SLOT)
1–WIRE SPEED SELECTION CODE
IF LOGIC 1, GENERATES STRONG PULLUP TO 5V IMMEDIATELY FOLLOWING THE
TIME SLOT
TYPE OF PULSE; 0 = STRONG PULLUP (5V), 1 = PROGRAMMING PULSE (12V)
1 = ARM STRONG PULLUP AFTER EVERY BYTE; 0 = DISARM
SEARCH ACCELERATOR CONTROL; 1 = ACCELERATOR ON, 0 = ACCELERATOR OFF
CONFIGURATION PARAMETER CODE (WRITE), 000 = READ CONFIGURATION
PARAMETER
CONFIGURATION PARAMETER VALUE CODE (WRITE), CONFIGURATION PARAMETER
CODE (READ)
DON’T CARE
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A master reset cycle can also be generated by means of software. This may be necessary if the host for
any reason has lost synchronization with the device. The DS2480B will perform a master reset cycle
equivalent to the power–on reset if it detects start polarity in place of the stop bit. The host has several
options to generate this condition. These include making the UART generate a break signal, sending a
NULL character at a data rate of 4800 bps and sending any character with parity enabled and selecting
space polarity for the parity bit. As with the power–on reset, the DS2480B requires a 1–Wire reset
command sent by the host at a data rate of 9600 bps for calibration.
After the DS2480B has reached the Command Mode, the host can send commands such as 1–Wire Reset,
Pulse, Configuration, Search Accelerator and Single Bit functions or switch over to the second static state
called Data Mode. In Data Mode the DS2480B simply converts bytes it receives at the TXD pin into
their equivalent 1–Wire wave forms and reports the results back to the host through the RXD pin. If the
Search Accelerator is on, each byte seen at TXD will generate a 12–bit sequence on the 1–Wire bus (see
section Search Accelerator for details). If the strong pullup to 5V is enabled (see Pulse command), each
byte on the 1–Wire bus will be followed by a pause of predefined duration where the bus is pulled to 5V
via a low impedance transistor in the 1–Wire driver circuit.
While being in the Data Mode the DS2480B checks each byte received from the host for the reserved
code that is used to switch back to Command Mode. To be able to write any possible code (including the
reserved one) to the 1–Wire bus, the transition to the Command Mode is as follows: After having
received the code for switching to Command Mode, the device temporarily enters the Check Mode
where it waits for the next byte. If both bytes are the same, the byte is sent once to the 1–Wire bus and
the device returns to the Data Mode. If the second byte is different from the reserved code, it will be
executed as command and the device finally enters the Command Mode. As a consequence, if the
reserved code that normally switches to Command Mode is to be written to the 1–Wire bus, this code
byte must be sent twice (duplicated). This detail must be considered carefully when developing software
drivers for the DS2480B.
After having completed a memory function with a device on the 1–Wire bus it is recommended to issue a
Reset Pulse. This means that the DS2480B has to be switched to Command Mode. The host then sends
the appropriate command code and continues performing other tasks. If during this time a device arrives
at the 1–Wire bus it will generate a presence pulse. The DS2480B will recognize this unsolicited presence
pulse and notify the host by sending a byte such as XXXXXX01b. The Xs represent undefined bit values.
The fact that the host receives the byte unsolicited together with the pattern 01b in the least significant 2
bits marks the bus arrival. If the DS2480B is left in Data Mode after completing a memory function
command it will not report any bus arrival to the host.
COMMAND CODE OVERVIEW
The DS2480B is controlled by a variety of commands. All command codes are 8 bits long. The most
significant bit of each command code distinguishes between communication and configuration
commands. Configuration commands access the configuration registers. They can write or read any of the
configurable parameters. Communication commands use data of the configuration register in order to
generate activity on the 1–Wire bus and/or (dis)arm the strong pullup after every byte or (de)activate the
Search Accelerator without generating activity on the 1–Wire bus. Details on the command codes are
included in the State Transition diagram (Figure 2). A full explanation is given in the subsequent sections
Communication Commands and Configuration Commands.
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In addition to the command codes explained in the subsequent sections the DS2480B understands the
following reserved command codes:
E1h
E3h
F1h
switch to Data Mode
switch to Command Mode
pulse termination
Except for these reserved commands, the Search Accelerator control and the first byte after power–on
reset or master reset cycle, every legal command byte generates a response byte. The pulse termination
code triggers the response byte of the terminated pulse command. Illegal command bytes do not generate
a command response byte.
Once the device is switched back from Data Mode to Command Mode one must not repeat the E3h
command while the Command Mode is still active.
COMMUNICATION COMMANDS
The DS2480B supports four communication function commands: Reset, Single Bit, Pulse, and Search
Accelerator control. Details on the assignment of each bit of the command codes are shown in Table 1.
The corresponding command response bytes are detailed in Table 2. The Reset, Search Accelerator
Control and Single Bit commands include bits to select the 1–Wire communication speed (regular,
flexible regular, Overdrive). Even if a command does not generate activity on the 1–Wire bus, these bits
are latched inside the device and will take effect immediately.
Reset
The Reset command must be used to begin all 1–Wire communication. The speed selection included in
the command code immediately takes effect. The response byte includes a code for the reaction on the 1–
Wire bus (bits 0 and 1) and a code for the chip revision (bits 2 to 4). If bit 5 of the response byte reads
‘1,’ a programming voltage is present on the VPP pin, indicating that one may try programming EPROM
devices.
Single Bit
The Single Bit command is used to generate a single time slot on the 1–Wire bus at the speed indicated by
bits 2 and 3. The type of the time slot (Write-0 or Write-1) is determined by the logic value of bit 4. A
Read Data time slot is identical to the Write-1 time slot. Bits 0 and 1 of the response byte transmitted by
the DS2480B at the end of the time slot reveal the value found on the 1–Wire bus when reading.
For a time slot without a subsequent strong pull–up, bit 1 of the command must be set to 0. For a time slot
immediately followed by a strong pullup bit 1 must be set to 1. As soon as the strong pullup is over, the
device will send a second response byte, code EFh (read 1) or ECh (read 0), depending on the value
found on the 1–Wire bus when reading. The strong pullup directly following the single bit is used in
conjunction with the crypto iButton.
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COMMUNICATION COMMAND CODES Table 1
FUNCTION
BIT 7
BIT 6
BIT 5 BIT 4
Single Bit
1
0
0
0 = write 0
1 = write 1
Search
Accelerator
Control
1
0
1
0 = accelerator off
1 = accelerator on
See Text
Reset
1
1
0
(don’t care)
BIT 3, BIT 2
BIT 1
00 reg. speed
01 flex. speed
10 OD. speed
11 reg. speed
00 reg. speed
01 flex. speed
10 OD. speed
11 reg. speed
00 reg. speed
01 flex. speed
10 OD. speed
See Text
BIT
0
1
0
1
0
1
11 pulse
See Text
1
BIT 2
BIT 1
BIT 0
1-Wire read back,
both bits same value
00 = 1-Wire shorted
01 = presence pulse
10 = alarming presence
pulse
11 = no presence pulse
undefined
11 reg. speed
Pulse
1
1
1
0 = 5V strong pullup
1 = 12V prog. pulse
COMMUNICATION COMMAND RESPONSE Table 2
FUNCTION BIT 7
Single Bit
1
BIT 6
0
BIT 5
0
BIT 4
0
Reset
1
1
See
Text
Pulse
1
1
1
BIT 3
same as sent
1
1
same as sent
(The Search Accelerator Control command does not generate a response byte.)
Search Accelerator Control
The Search Accelerator Control command is used to set or reset the Search Accelerator control flag. Bit 4
of the command code contains the state to which the accelerator control flag is to be set. If the flag is set
to a 1 (on) the device translates every byte received in Data Mode into a 12–bit sequence on the 1–Wire
bus. For details on how the Search Accelerator works please refer to the section Search Accelerator
Operation. Before activating the Search Accelerator, one must make sure that the strong pullup after
every byte is disarmed (see Pulse Command). The Search Accelerator command does not generate a
command response byte.
Although the Search Accelerator Control command itself does not generate any 1–Wire activity, it can be
used to select the communication speed on the 1–Wire bus. The speed selection (if different from the
previous setting, e.g., from a Reset command) will take effect immediately.
Pulse
The Pulse command serves several functions that are selected by the contents of bit 1 and bit 4 of the
command code. The main functions are generating a strong pullup to 5V and generating 12V
programming pulses for EPROM devices (if the 12V are available at the VPP pin). The secondary function
of the pulse command is arming and disarming a strong pullup after every subsequent byte in Data Mode.
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The arm/disarm function is controlled by bit 1 of the command code. Bit 4 determines whether the device
will generate a strong pullup to 5V or a 12V programming pulse. The table below summarizes these
options.
BIT 4
0
1
0
1
BIT 1
0
0
1
1
FUNCTION
strong pullup to 5V and disarm
12V programming pulse and disarm
strong pullup to 5V and arm
12V programming pulse and arm
The strong pullup to 5V is required to program EEPROM devices or to operate special function devices
that require a higher current for a limited time after having received a “go and convert” command.
Therefore and because it significantly reduces the effective data throughput on the 1–Wire bus, the strong
pullup is disarmed most of the time. Although arming or disarming is simultaneously possible while
generating a programming pulse, this is not recommended since it is likely to destroy the DS2480B if
non–EPROM devices are connected to the 1–Wire bus.
The duration of the strong pullup or programming pulse is determined by configuration parameters and
ranges from a few microseconds over “dynamic” duration (strong pullup only) up to unlimited (see
section Configuration Commands). However, unlimited duration is not allowed in conjunction with
arming the strong pullup after every byte. As long as the DS2480B is in Command Mode the host may
terminate a strong pullup or programming pulse prematurely at any time by sending the command code
F1h.
The response byte is generated as soon as the strong pullup or programming pulse is over (either because
the predefined time has elapsed, the high current demand is over, or due to termination by the host). The
response byte mainly returns the command code as sent by the host, but the 2 least significant bits are
undefined.
If the strong pullup is armed and the device is in Data Mode, the end of the strong pullup will be signaled
as code F6h if the most significant bit of the preceding data byte on the 1–Wire bus is a 1 and 76h
otherwise. The host will see this response byte in addition to the response on the data byte sent (see also
section Wave Forms later in this document).
SEARCH ACCELERATOR INTRODUCTION
The Search Accelerator is a logic block inside the DS2480B that allows using the Search ROM function
very efficiently under modern operating systems such as Windows and Windows 95/NT. Without the
DS2480B all 1–Wire port adapters have to involve the computer’s CPU for every single time slot or pulse
to be generated on the 1–Wire bus.
Under DOS, accessing peripherals such as the UART or parallel port is very straight forward and
therefore fast. Under Windows the situation is different and it may take several milliseconds or more to
get the first time slot generated on the 1–Wire bus. Every subsequent time slot will be generated in much
less time, since the computer simply sends out “streams”− a long chain of bytes. This works reasonably
well when reading or writing large blocks of data.
Searching the 1–Wire bus to identify all ROM IDs of the devices connected, however, requires reading 2
bits, making a decision and then writing a bit. This procedure is to be repeated 64 times to identify and
address a single device. With the overhead of modern operating systems this fairly simple process takes a
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lot of time, reducing the discovery rate of devices on the 1–Wire bus from a typical value of 40 to 50 per
second under DOS to less than 10 under Windows. To solve this problem the Search Accelerator was
developed.
During the execution of the Search ROM function, the Search Accelerator receives from the host
information on the preferred path to choose as one contiguous chain of bytes and then translates it into the
appropriate time slots on the 1–Wire bus. In addition, the Search Accelerator reports back to the host the
ROM ID of the device actually addressed and the bit positions in which conflicts were found. (If the
ROM ID of one device has a 0 in a bit position where another device has a 1, this is called a “conflict” on
the electrical level and “discrepancy” on the logical level. See the Book of DS19xx iButton Standards for
a more detailed discussion of the Search ROM.) This helps the host to select the preferred path for the
next Search ROM activity.
Since the ROM ID of all MicroLAN compatible devices is 64 bits long and a conflict may occur in any of
these bits, the total length of data reported to the host is 128 bits or 16 bytes. To avoid data overrun (if the
CPU sends data faster than it can be processed) the protocol for the Search Accelerator operation was
defined so that one has to send as many bytes as one will receive. This way the CPU sends 16 bytes for
each path and the UART guarantees the correct data timing and frees the CPU for other tasks while the
DS2480B performs a Search ROM function.
SEARCH ACCELERATOR OPERATION
After the Search Accelerator is activated and the Data Mode is selected, the host must send 16 bytes to
complete a single Search ROM pass on the 1–Wire bus. These bytes are constructed as follows:
first byte
7
6
r3
x3
et cetera
16th byte
7
6
r63
x63
5
r2
4
x2
3
r1
2
x1
1
r0
0
x0
5
r62
4
x62
3
r61
2
x61
1
r60
0
x60
In this scheme, the index (values from 0 to 63, “n”) designates the position of the bit in the ROM ID of a
MicroLAN compatible device. The character “x” marks bits that act as filler and do not require a specific
value (don’t care bits). The character “r” marks the path to go at that particular bit in case of a conflict
during the execution of the ROM Search.
For each bit position n (values from 0 to 63) the DS2480B will generate three time slots on the 1–Wire
bus. These are referenced as:
b0
b1
b2
for the first time slot (Read Data)
for the second time slot (Read Data) and
for the third time slot (Write Data).
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The type of time slot b2 (write 1 or write 0) is determined by the DS2480B as follows:
b2
= rn if conflict (as chosen by the host)
= b0 if no conflict (there is no alternative)
= 1 if error (there is no response)
The response the host will receive during a complete pass through a Search ROM function using the
Search Accelerator consists of 16 bytes as follows:
first byte
7
6
r’3
d3
et cetera
16th byte
7
6
r’63
d63
5
r’2
4
d2
3
r’1
2
d1
1
r’0
0
d0
5
r’62
4
d62
3
r’61
2
d61
1
r’60
0
d60
As before, the index (values from 0 to 63, “n”) designates the position of the bit in the ROM ID of a
MicroLAN compatible device. The character “d” marks the discrepancy flag in that particular bit
position. The discrepancy flag will be 1 if there is a conflict, or no response in that particular bit position,
and 0 otherwise. The character “r” marks the actually chosen path at that particular bit position. The
chosen path is identical to b2 for the particular bit position of the ROM ID.
To perform a Search ROM sequence one starts with all bits rn being 0s. In case of a bus error, all
subsequent response bits r’n are 1s until the Search Accelerator is deactivated. Thus, if r’63 and d63 are both
1, an error has occurred during the search procedure and the last sequence has to be repeated. Otherwise
r’n (n = 0 ... 63) is the ROM code of the device that has been found and addressed.
For the next Search ROM sequence one reuses the previous set rn (n = 0 ... 63) but sets rm to 1 with “m”
being the index number of the highest discrepancy flag (that is, 1) and sets all ri to 0 with i > m. This
process is repeated until the highest discrepancy occurs in the same bit position for two consecutive
passes.
The table below shows an example for the communication between host and DS2480B to perform one
pass through the Search ROM function using the Search Accelerator. After a device has been identified
and addressed, a memory function (not specified here) is executed and finally a reset pulse is generated.
This example assumes that the DS2480B was in Command Mode and that regular 1–Wire speed is used.
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Search Accelerator Usage Example
Action Sequence
Generate Reset Pulse
Set Data Mode
Search ROM command
Set Command Mode
Search Accelerator On
Set Data Mode
Send 16 bytes
Set Command Mode
Search Accelerator Off
Set Data Mode
Do Memory Function
Set Command Mode
Generate Reset Pulse
Host TX
C1
E1
F0
E3
B1
E1
data
E3
A1
E1
Host RX
CD
(nothing)
(as sent)
(nothing)
(nothing)
(nothing)
(response)
(nothing)
(nothing)
(nothing)
E3
C1
(nothing)
CD
CONFIGURATION COMMANDS
The DS2480B is designed to be configurable for the varying requirements of its application. When the
device powers up and/or performs a master reset cycle, the hard–wired default configuration settings take
effect. These settings will work on a short 1–Wire bus and assume regular 1–Wire communication speed.
To change these default settings and to verify the current settings, the logic of the DS2480B supports
configuration commands. A summary of the available configuration parameters, their default settings at
regular and Overdrive speed and their applicability is shown in Table 3.
Parameters not related to the communication speed on the 1–Wire bus specify the duration of the 12V
programming pulse, the duration of the strong pull–up to 5V, the threshold current of the load sensor for
“dynamic” strong pullup duration, and the baud rate on the interface that connects the DS2480B to the
host. The remaining three parameters are used to modify the 1–Wire communication wave forms if one
selects “Flexible Speed” (see “Communication Commands” for speed selection).
Flexible speed is implemented to improve the performance of large MicroLAN Networks. This is
accomplished by:
• limiting the slew rate on falling edges (e. g., at the beginning of time slots, to reduce ringing),
• extending the Write-1 low time (allows the current flow through the network to end slowly, to prevent
voltage spikes from inductive kickback),
• delaying the time point when reading a bit from the 1–Wire bus (gives the network more time to
stabilize, to get a higher voltage margin) and
• adding extra recovery time between Write-0 time slots (allows more energy transfer through the
network, to replenish the parasite power supply of the devices on the bus).
The latter two functions are controlled by a single parameter. Taking advantage of flexible speed requires
changing one or more of these parameters from their default values. Otherwise the waveforms will be
identical to those at regular speed.
Each configuration parameter is identified by its 3–bit parameter code and can be programmed for one of
a maximum eight different values using a 3–bit value code. A matrix of parameter codes and value codes
with the associated physical values in shown in Table 4.
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CONFIGURATION PARAMETER OVERVIEW Table 3
Parameter Description
Pull-Down Slew Rate
Control
Programming Pulse
Duration
Strong Pullup Duration
Write-1 Low Time
Data Sample Offset and
Write 0 Recovery Time
Load Sensor Threshold
RS232 Baud Rate
Par. Code
001
Configurable at
Regular Flexible Overdrive
v
Default
Reg./Flex. Overdrive
15 V/µs
15 V/µs
010
v
v
v
512 µs
512 µs
011
100
101
v
v
v
v
v
110
111
v
v
v
v
v
v
524 ms
8 µs
3 µs
3 µs
3 mA
9.6k bits/s
524 ms
1 µs
1 µs
3 µs
3 mA
9.6k bits/s
The numbers given for parameter 001 (Pulldown Slew Rate Control) are nominal values. They may vary
to some extent and are almost independent of the load on the 1–Wire bus. Information on how to select
the optimum value of this parameter is given in section “Controlled Edges."
Parameter 110 (Load Sensor Threshold) has been implemented in order to more efficiently support the
high current demand of the crypto iButton. The load sensor is only active if “dynamic” (value code 110)
for the Strong Pullup Duration (parameter 011) has been selected. The nominal and default value for the
load sensor threshold is 3.0 mA with a tolerance band of -25% to +80%. The sensor threshold should be
left at its default value; changes should only be made to compensate for tolerances. Dynamic duration
should only be used when operating crypto iButtons and not for gang-programming 1-Wire EEPROMs or
measuring temperature with multiple temperature sensors converting simultaneously.
For the parameters 010 (Programming Pulse Duration) and 011 (Strong Pullup Duration) one may select
indefinite duration. This value, however, should only be selected if one is not going to switch the device
to Data Mode. As long as the device stays in Command Mode, any pulse function (programming or
strong pullup) that uses one of these parameters can be terminated by sending the command code F1h.
Termination is not possible if the device is in Data Mode.
Parameter 111 (RS232 Baud Rate) has two functions. It selects the baud rate and allows inversion of the
signal at the RXD pin. Using one of the value codes 100 to 111 will set the polarity at RXD to the
opposite of what is defined by the logic level at the POL pin (asymmetry bit, see Figure 1). This may
reduce the component count in some applications of the device. Note that when changing the baud rate,
the DS2480B will send the command response byte at the new data rate.
A short explanation on the use of parameters 100 (Write-1 Low Time) and 101 (Data Sample
Offset/Write-0 Recovery Time) is given in the section “Timing Diagrams” later in this document.
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CONFIGURATION PARAMETER VALUE CODES Table 4
Parameter Code
001 (PDSRC)
010 (PPD)
000
15
32
001
2.2
64
010
1.65
128
Value Codes
011
100
101
1.37
1.1
0.83
256
512 1024
110
0.7
2048
111
0.55
∞
Unit
V/µs
µs
011 (SPUD)
16.4
65.5
131
262
524
1048
“dyn.”
ms
100 (W1LT)
101 (DSO/W0RT)
110 (LOAD)
111 (RBR)
8
3
1.8
9.6
9
4
2.1
19.2
10
5
2.4
57.6
11
6
2.7
115.2
12
7
3.0
9.6
13
8
3.3
19.2
14
9
3.6
57.6
∞
15
10
3.9
115.2
µs
µs
mA
kbits/s
The syntax of configuration commands is very simple. Each 8–bit code word contains a 3–bit parameter
code to specify the parameter and the 3–bit value code to be selected. Bit 7 of the command code is set to
0 and bit 0 is always a 1. To read the value code of a parameter, one writes all 0s for the parameter code
and puts the parameter code in place of the parameter value code. Table 5 shows the details.
The configuration command response byte is similar to the command byte itself. Bit 0 of the response
byte is always 0. When writing a parameter, the upper 7 bits are the echo of the command code. When
reading a parameter, the current value code is returned in bit positions 1 to 3 with the upper 4 bits being
the same as sent (see Table 6).
CONFIGURATION COMMAND CODES Table 5
FUNCTION
Write Parameter
Read Parameter
BIT 7
0
0
BIT 6
BIT 5
BIT 4
parameter code
0
0
0
BIT 3
BIT 2
BIT 1
parameter value code
parameter code
BIT 0
1
1
CONFIGURATION COMMAND RESPONSE BYTE Table 6
FUNCTION
Write Parameter
Read Parameter
BIT 7
0
0
BIT 6
BIT 5
BIT 4
same as sent
same as sent
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BIT 3
BIT 2
BIT 1
same as sent
parameter value code
BIT 0
0
0
101999
DS2480B
CONTROLLED EDGES
One of the tasks of the DS2480B is to actively shape the edges of the 1–Wire communication waveforms.
This speeds up the recharging of the 1–Wire bus (rising edges) and reduces ringing of long lines (falling
edges). The circuitry for shaping rising edges is always on. The slew rate of falling edges is actively
controlled only at flexible speed and requires the parameter for slew rate control being different from its
power–on default value.
All Rising Edges
The active pullup of the rising edges reduces the rise time on the 1–Wire bus significantly compared to a
simple resistive pullup. Figure 4 shows how the DS2480B is involved in shaping a rising edge.
ACTIVE PULLUP Figure 4
The circuit operates as follows: At t1 the pulldown (induced by the DS2480B or a device on the bus) ends.
From this point on the 1–Wire bus is pulled high by the weak pullup current IWEAKPU provided by the
DS2480B. The slope is determined by the load on the bus and the value of the pullup current. At t2 the
voltage crosses the threshold voltage VIAPO. Now the DS2480B switches over from the weak pullup
current IWEAKPU to the higher current IACTPU. As a consequence, the voltage on the bus now rises faster. As
the voltage on the bus crosses the threshold VIAPTO at t3, a timer is started. As long as this timer is on
(tAPUOT), the IACTPU current will continue to flow. After the timer is expired, the DS2480B will switch
back to the weak pullup current.
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DS2480B
Falling Edges (DS2480B–initiated)
Whenever the DS2480B begins pulling the 1–Wire bus low to initiate a time slot, for example, it first
turns off the weak pullup current IWEAKPU. Then, at regular and Overdrive speeds it will generate a falling
edge at a slew rate of typically 15V/µs. This value is acceptable for short 1–Wire busses and adequate for
communication at Overdrive speed. For MicroLAN networks of more than roughly 30 meters length one
should always use flexible speed. One of the parameters that is adjustable at flexible speed is the slew rate
of DS2480B–initiated falling edges. The effect of the slew rate control is shown in Figure 5.
SLEW RATE CONTROL Figure 5
As extensive tests have shown, MicroLAN networks at a length of up to 300 meters will perform best if
the fall time tF is in the range of 4 ± 0.5 µs. This translates into a slew rate of approximately 1V/µs. This
slew rate is typically achieved by setting the configuration parameter 001 (Pulldown Slew Rate Control)
to a value of 100 (see Table 4). If the actual measured fall time is longer than the target value, one should
use a value code of 011 or lower. If the fall time is shorter, one should use a value code of 101 or higher.
Once determined, the value code for the Pulldown Slew Rate Control parameter should be stored in the
host and always be loaded into the DS2480B after a power–on or master reset cycle.
TIMING DIAGRAMS
This section explains the wave forms generated by the DS2480B on the 1–Wire bus in detail. First the
communication wave forms such as the Reset/Presence Detect Sequence and the time slots are discussed.
After that follows a detailed description of the pulse function under various conditions. The wave forms
as generated by the DS2480B may deviate slightly from specifications found in the “Book of DS19xx
iButton Standards” or in data sheets of 1–Wire slave devices. However, at a closer look one will find that
all of the timing requirements are met.
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DS2480B
1–WIRE COMMUNICATION WAVE FORMS
One of the major features of the DS2480B is that it relieves the host from generating the timing of the 1–
Wire signals and sampling the 1–Wire bus at the appropriate times. How this is done for the
reset/presence detect sequence is shown in Figure 6a. This sequence is composed of four timing
segments: the reset low time tRSTL, the short/interrupt sampling offset tSI, the presence detect sampling
offset tPDT and a delay time tFILL. The timing segments tSI, tPDT and tFILL comprise the reset high time tRSTH
where 1–Wire slave devices assert their presence or interrupt pulse. During this time the DS2480B pulls
the 1–Wire bus high with its weak pullup current.
The values of all timing segments for all 1–Wire speed options are shown in the table. Since the
reset/presence sequence is slow compared to the time slots, the values for regular and flexible speed are
the same. Except for the falling edge of the presence pulse all edges are controlled by the DS2480B. The
shape of the uncontrolled falling edge is determined by the capacitance of the 1–Wire bus and the
number, speed and sink capability of the slave devices connected.
RESET/PRESENCE DETECT Figure 6a
Speed
Regular
Overdrive
Flexible
tRSTL
512 µs
64 µs
512 µs
tSI
8 µs
2 µs
8 µs
tPDT
64 µs
8 µs
64 µs
tFILL
512 µs
64 µs
512 µs
tRSTH
584 µs
74 µs
584 µs
After having received the command code for generating a reset/presence sequence, the DS2480B pulls
the 1–Wire bus low for tRSTL and then lets it go back to 5V. The DS2480B will now wait for the
short/interrupt sampling offset tSI to expire and then test the voltage on the 1–Wire bus to determine if
there is a short or an interrupt signal. If there is no short or interrupt (as shown in the picture), the
DS2480B will wait for tPDT and test the voltage on the 1–Wire bus for a presence pulse. Regardless of the
result of the presence test, the DS2480B will then wait for tFILL to expire and then send the command
response byte to the host.
If the test for interrupt or short reveals a logic 0, the DS2480B will wait for 4096 µs and then test the 1–
Wire bus again. If a logic 0 is detected, the 1–Wire bus is shorted and a command response byte with the
code for SHORT will be sent immediately. If a logic 1 is detected, the device will wait for tFILL to expire,
after which it will send the command response byte with the code for an alarming presence pulse. No
additional testing for a presence pulse will be done. The DS2480B will perform the short/interrupt testing
as described also at Overdrive speed, although interrupt signaling is only defined for regular speed.
The idle time following the Reset/Presence Detect sequence depends on the serial communication speed
and the host’s response time.
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DS2480B
A Write-1 and Read Data time slot is comprised of the segments tLOW1, tDSO and tHIGH. During Write-1
time slots, after the Write-1 low time tLOW1 is over, the DS2480B waits for the duration of the data sample
offset and then samples the voltage at the 1–Wire bus to read the response. After this, the waiting time
tHIGH1 must expire before the time slot is complete. A Write-0 time slot only consists of the two segments
tLOW0 and tREC0.
If the network is large or heavily loaded, one should select flexible speed and extend tLOW1 to more than 8
µs to allow the 1–Wire bus to completely discharge. Since a large or heavily loaded network needs more
time to recharge, it is also recommended to delay sampling the bus for reading. A higher value for tDSO
will increase the voltage margin and also provide extra energy to the slave devices when generating a
long series of write 0 time slots. However, the total of tLOW1 + tDSO should not exceed 22 µs*. Otherwise
the slave device responding may have stopped pulling the bus low when transmitting a logic 0.
The idle time between time slots within a byte or during a 12–bit sequence while the Search Accelerator
is on is 0. Between bytes, 12–bit search sequences and single bits the idle time depends on the RS232
data rate and the host’s response time. The response byte is sent to the host as soon as the last time slot of
a byte, 12–bit sequence or the command is completed.
WRITE-1 AND READ DATA TIME SLOT Figure 6b
Speed
Regular
Overdrive
Flexible
tLOW1
8 µs
1 µs
8 to 15 µs
tDSO
3 µs
1 µs
3 to 10 µs
tHIGH1
49 µs
8 µs
49 µs
tSLOT*
60 µs
10 µs
60 to 74 µs
WRITE-0 TIME SLOT Figure 6c
Speed
Regular
Overdrive
Flexible
tLOW0
57 µs
7 µs
57 µs
tREC0
3 µs
3 µs
3 to 10 µs
tSLOT*
60 µs
10 µs
60 to 67 µs
*In a 5V environment (± 1V, full temperature range) the tolerance of the internal time base of 1–Wire
slave devices is much narrower than what it is when operated at the minimum voltage of 2.8V. Therefore,
the timing generated by the DS2480B is in compliance with the requirements of all MicroLAN–
compatible 1–Wire devices.
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DS2480B
PULSE WAVE FORMS, DISARMED
The Pulse command can be used to generate a strong pullup to 5V and a 12V programming pulse,
respectively. The duration of the pulse is predefined if the parameter value code of parameter 010
(Programming Pulse Duration) has a value from 000 to 110, and parameter 011 (Strong Pullup Duration)
has a value from 000 to 101 (see Table 4). Figures 7a and 7b show the timing of a pulse with predefined
duration, which should be considered the normal case. With dynamic duration the pulse ends as soon as
the current demand of the slave devices on the bus falls below the threshold of the load sensor. If infinite
duration is chosen (parameter value code 111), the host must terminate the Pulse command, as shown in
Figures 7c and 7d. All versions of Figure 7 assume that bit 1 of the pulse command is 0, i.e., disarmed
mode. See section Communication Commands, Pulse, for more details on possibilities of the Pulse
command.
STRONG PULLUP TO 5V, PREDEFINED DURATION Figure 7a
The processing of a pulse command is essentially the same, regardless if a strong pullup or a
programming pulse is requested. At t1 the host starts sending the pulse command byte. At t2 the DS2480B
has received the command and immediately generates the pulse. The pulse ends at t3 and the DS2480B
sends out the command response byte to inform the host that the command is completed. The idle time
between t1 and t2 is determined by the time to transmit the command byte at the selected baud rate. The
idle time between t3 and t4 is comprised of the time to transmit the response byte, plus the response time
of the host plus the time to transmit the command and/or data to generate the next time slot.
12V PROGRAMMING PULSE, PREDEFINED DURATION Figure 7b
A correct programming pulse can only be generated if the 12V programming voltage is available at the
VPP pin of the DS2480B. The rising and falling edges of the programming pulse are actively controlled by
DS2480B. The slew rate is approximately 14V/µs and meets the requirements of 1-Wire EPROM
devices.
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DS2480B
For EPROM programming, only a single slave device should be connected to the 1–Wire bus and the
cable must to be short, not to exceed a few meters. One should not attempt generating a programming
pulse with a non-EPROM device on the bus; this may damage the device as well as the DS2480B.
Certain applications may require a duration for a strong pullup or programming pulse that cannot be
realized using one of the predefined values. Selecting infinite duration allows the host to generate pulses
of any length. As a consequence, however, the host becomes responsible to actively control the duration
of the pulse. Failing to do so may require a power–on reset or master reset cycle of the DS2480B. For
this reason, infinite duration should only be used if absolutely necessary.
The time to end a pulse of infinite duration strongly depends on the baud rate of the communication
between host and DS2480B. Neglecting the response time of the host, the minimum pulse durations are:
86.8 µs at 115.2 kbps, 173.6 µs at 57.6 kbps, 520 µs at 19.2 kbps and 1.04 ms at 9.6 kbps.
STRONG PULLUP TO 5V, INFINITE DURATION Figure 7c
As before, processing the command is essentially the same, regardless if it is for a strong pullup or a
programming pulse. At t1 the host starts sending the Pulse command byte. At t2 the DS2480B has
received the command and immediately activates the strong pullup or switches in the 12V programming
voltage. To end the pulse, the DS2480B must receive a Termination command, code F1h, which occurs at
t3. The Termination command does not generate a response byte. The DS2480B will immediately end the
pulse and send out the response byte of the pulse command. The idle time between t1 and t2 is determined
by the time to transmit the command byte at the selected baud rate. The idle time between t3 and t4 is
comprised of the time to transmit the pulse response byte, plus the response time of the host plus the time
to transmit the command and/or data to generate the next time slot.
12V PROGRAMMING PULSE, INFINITE DURATION Figure 7d
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DS2480B
PULSE WAVE FORM, ARMED
As explained in section Communication Commands, bit 1 of the Pulse command allows the arming of a
strong pullup to 5V if the bit is set to 1. If the strong pullup is armed and the device is switched to Data
Mode, there will be a strong pullup immediately following every byte on the 1–Wire bus. This mode is
implemented to provide extra energy when writing to EEPROM devices or to do a temperature
conversion with the DS1920 Temperature iButton, for example. These devices need a strong pullup
immediately after the power–consuming activity has been initiated by a command code.
To arm the strong pull–up, one usually generates a “dummy” pulse with bit 1 being 1 while the device is
in Command Mode. To save time, the dummy pulse may immediately be terminated by sending the
Termination command, code F1h. Then one switches to Data Mode and sends a command code that
makes one or more slaves on the 1–Wire bus require extra energy. After the command execution is
finished, one switches back to Command Mode and disarms the strong pullup by generating another
dummy pulse. A complete temperature conversion sequence that shows the use of the armed pulse is
included in Section “Software Driver Examples”.
STRONG PULLUP TO 5V, ARMED, PREDEFINED DURATION Figure 8
Figures 8 shows the timing of the strong pullup in Data Mode. At t1 the 8th time slot of the byte sent to the
1–Wire bus is completed. Without any delay the DS2480B now activates the strong pullup and
simultaneously starts sending the data response byte to the host. At t2 the strong pullup ends and the
DS2480B sends a pulse response byte to the host. The idle time between t2 and t3 is comprised of the time
to transmit the pulse response byte, plus the response time of the host plus the time to transmit the
command and/or data to generate the next time slot. Since in Data Mode the Pulse Termination command
is not applicable, the duration of the strong pullup must be limited. See Table 4, parameter 011 (Strong
Pull–Up Duration) for details.
Dynamic duration is permissible in conjunction with the armed pulse function. However, the load sensor
does not have the sensitivity required for detecting when the high current demand of a single 1-Wire
temperature sensor or EEPROM device ends. Since the duration of the high current demand of such devices depends on temperature and is slightly different for every individual device, even with multiple
EEPROMs or temperature sensors operating simultaneously, dynamic duration should not be used.
Infinite duration, if accidentally selected, will require a power–on or master reset cycle to get the
DS2480B back to communicating with the host.
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DS2480B
SINGLE BIT WITH STRONG PULLUP
Similar to the Pulse command, the Single Bit command also allows generating a strong pullup
immediately following a time slot. The strong pullup of the Single Bit command, however, is controlled
directly by bit 1 of the command code and therefore needs not be armed. Since the DS2480B remains in
Command Mode when using the Single Bit command, any duration of the strong pullup including
dynamic as well as infinite may be selected.
Strong pullup immediately following a single time slot is used in conjunction with the crypto iButton.
Under certain conditions the crypto iButton sends out a single bit and then immediately starts executing a
firmware program. This raises the energy demand significantly until the program comes to a halt, at
which point the host computer has to be interrupted. The dynamic duration option of the strong pullup
supplies energy for any duration as needed and automatically notifies the host that the crypto iButton is
ready for the next command.
SINGLE BIT WITH STRONG PULLUP, PREDEFINED DURATION Figure 9a
Figure 9 shows the timing of the Single Bit command immediately following strong pullup. For
predefined and dynamic duration (Figure 9a) the timing is as follows: At t1 the time slot is completed.
Now the DS2480B activates the strong pullup and simultaneously starts sending the response byte of the
Single Bit command to the host. At t2 the strong pullup ends and the DS2480B sends out a pulse response
byte. The idle time between t2 and t3 is comprised of the time to transmit the pulse response byte, plus the
response time of the host plus the time to transmit the command and/or data to generate the next time slot.
SINGLE BIT WITH STRONG PULLUP, INFINITE DURATION Figure 9b
For infinite duration (Figure 9b) the strong pullup also begins immediately after the time slot is
completed. To end the strong pullup, the DS2480B must receive a Termination command, code F1h,
which occurs at t2. The termination command does not generate a response byte. The DS2480B will then
immediately end the strong pullup and send out a pulse response byte. Everything else is the same as with
predefined duration.
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DS2480B
The minimum duration of a strong pullup of infinite duration strongly depends on the baud rate of the
communication between host and DS2480B. The host must first receive the response byte of the Single
Bit command, react to it and then transmit the termination command. Neglecting the host’s response time,
the shortest duration of an infinite strong pullup therefore is 173.6 µs at 115.2 kbps, 347.2 µs at 57.6
kbps, 1.04 ms at 19.2 kbps and 2.08 ms at 9.6 kbps.
SOFTWARE DRIVER EXAMPLES
The DS2480B requires a software driver that translates the activities to be generated on the 1–Wire bus
into the appropriate commands. The examples below cover typical situations, such as reading the ROM,
writing to the scratchpad of a Memory iButton, reading the memory of a Memory iButton, programming
an Add–Only iButton EPROM and performing a temperature conversion with the Temperature iButton
DS1920. An example for the use of the Search Accelerator is included in the description of the Search
Accelerator, earlier in this document.
The DS2480B command codes used in these examples are valid for regular speed and will work properly
on short 1–Wire busses (< 10 meters). The response byte on the reset command assumes a normal
presence pulse, no alarm or short.
The DS2480B includes a 1–byte buffer that stores a byte received from the host while the previous byte is
being translated into activity on the 1–Wire bus. For this reason the host may send another byte even
without having received the response byte. Sending bytes faster than they can be translated into 1–Wire
activities may result in loss of data and/or synchronization and therefore should be avoided.
READ ROM SEQUENCE
Action Sequence
Generate Reset Pulse
Set Data Mode
Read ROM Command
Read ROM ID (8 bytes)
Set Command Mode
Generate Reset Pulse
Host TX
C1
E1
33
FF (x8)
E3
C1
Host RX
CD
(nothing)
(as sent)
ROM ID
(nothing)
CD
Write 2 bytes to scratchpad at memory locations 16h and 17h
Action Sequence
Host TX
Generate Reset Pulse
C1
Set Data Mode
E1
Skip ROM Command
CC
Write Scratchpad Command
0F
Starting Address TA1
16
Starting Address TA2
00
Write to the Scratchpad
(2 bytes)
Set Command Mode
E3
Generate Reset Pulse
C1
Host RX
CD
(nothing)
CC
(as sent)
(as sent)
(as sent)
(as sent)
(nothing)
CD
WRITE SCRATCHPAD SEQUENCE
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DS2480B
READ MEMORY SEQUENCE
Action Sequence
Generate Reset Pulse
Set Data Mode
Skip ROM Command
Read Memory Command
Starting Address TA1
Starting Address TA2
Read 8 Bytes of Data
Set Command Mode
Generate Reset Pulse
Host TX
C1
E1
CC
F0
40
00
FF (x8)
E3
C1
Host RX
CD
(nothing)
CC
(as sent)
(as sent)
(as sent)
(data)
(nothing)
CD
WRITE EPROM SEQUENCE (DS2505)
Write memory starting at address 40h
Action Sequence
Host TX
Set Vpp dur. = 512 µs
29
Generate Reset Pulse
C1
Set Data Mode
E1
Skip ROM Command
CC
Write Memory Command
0F
Starting Address TA1
40
Starting Address TA2
00
*** Send Data Byte
(data)
Receive CRC16
FF (x2)
Set Command Mode
E3
Generate Program Pulse
FD
Set Data Mode
E1
Read Written Byte
FF
Go to *** to write the next byte or end the sequence as shown below
Set Command Mode
E3
Generate Reset Pulse
C1
Host RX
28
CD
(nothing)
(as sent)
(as sent)
(as sent)
(as sent)
(as sent)
CRC16
(nothing)
response
(nothing)
(data)
(nothing)
CD
TEMPERATURE CONVERSION SEQUENCE
Action Sequence
Set pullup dur. = 524 ms
Generate Reset Pulse
Set Data Mode
Skip ROM Command
Set Command Mode
Arm Strong Pullup
Terminate Pulse
Set Data Mode
Convert Temperature
Wait for Pulse Response
Set Command Mode
Disarm Strong Pullup
Terminate Pulse
Generate Reset Pulse
Host TX
39
C1
E1
CC
E3
EF
F1
E1
44
(nothing)
E3
ED
F1
C1
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Host RX
38
CD
(nothing)
(as sent)
(nothing)
(nothing)
response
(nothing)
(as sent)
response
(nothing)
(nothing)
response
CD
101999
DS2480B
HARDWARE APPLICATION EXAMPLES
This section discusses five typical application scenarios. The DS2480B can be configured for EPROM
programming as well as for 5V operation only. In either case special care must be taken to ensure that the
voltage at the VPP pin is higher than the voltage at the VDD pin. For 5V operation this is accomplished by
connecting the VPP pin directly to the power supply and feeding VDD through a Schottky diode, as shown
in Figure 10a. For EPROM programming the 5V supply for the DS2480B is derived from the 12V
programming voltage through a separate 5V regulator.
To protect the 1-Wire port of the DS2480B from electrostatic discharge it is recommended to use a lowcapacitance ESD protection diode, such as the DS9502. For 5V operation a single device is sufficient. For
EPROM programming two DS9502s must be connected in series to achieve a high enough breakdown
voltage.
When directly designed into a new product, the device can be connected as shown in Figure 10a. The
circuit becomes more complex if a 1–Wire bus is to be interfaced to a port that provides and expects
inverted signals, but does not necessarily meet the RS232C (± 12V) standard (Figure 10b).
UART DIRECT Figure 10a
With EPROM Programming
12 V
VDD
VPP
POL
UART
5V
RXD
or µC
1-W
DS2480
SOUT (TXD)
RXD
1-W
*
TXD
GND
GND
Return
M
0
POL
DS2480
TXD
1
L
VDD
VPP
1-Wire Bus
SIN (RXD)
Start
5V Operation Only
5V
Regulator
Stop
* only one DS9502 ESD protection diode with 5V
+/- 5V RS232 Figure 10b
*
* DS9502; see text
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DS2480B
The signals DTR and RTS provide the power to operate the DS2480B. The resistor in the TXD line and
the Schottky diode limit the negative voltage at the TXD pin of the DS2480B to 0.3V maximum. The
resistor is typically 4.7 kΩ . If the inverting driver is current–limited to 1 mA the resistor is not required.
From the DS2480B’s perspective, this circuit will work with inverted signals of ± 5V as well as 0 to 5V.
Depending on the voltage levels the host expects, it may be necessary to generate a negative voltage on
the RXD line. Figure 10c shows how this can be accomplished for a true RS232C system.
± 12V RS232 Figure 10c
*
* DS9502; only one device needed for 5V operation
In the interface to a true RS232C system (± 12V, Figure 10c) the power for the DS2480B is stolen from
DTR and RTS. The software must make sure that at least one of these signals constantly provides the 12V
operating voltage. The 6.8 kΩ resistor and the 4.7 V Zener diode in the TXD line limit the positive
voltage at the TXD pin of the DS2480B. The Schottky diode limits the negative voltage to 0.3V
maximum. The Schottky diode in series with capacitor forms a parasitic supply to generate the negative
bias for the host’s receive channel. The positive signal is switched in through the P–channel MOSFET
that connects to the RXD output of the DS2480B. In this circuit diagram the MOSFET switches the RXD
line to +5V, which normally is sufficient for RS232C systems.
Switching to 12V is also possible, but requires a P–channel transistor with a different threshold voltage.
The signal inversion caused by the transistor is compensated through the DS2480B by using a value code
of 100, 101, 110 or 111 for the RS232 baud rate setting.
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UART DIRECT OPTO-ISOLATED Figure 10d
*
* DS9502; only one device needed for 5V operation
The circuit in Figure 10d is essentially the same as in Figure 10a. The main difference is the opto–
isolation. The characteristics of the opto–isolators are not very critical. Using a different type will affect
the values of the resistors that limit the current through the LEDs and bias the photo transistors.
± 5 TO 12V RS232 OPTO-ISOLATED Figure 10e
*
* DS9502; only one device needed for 5V operation
The circuit in Figure 10e combines the true RS232C interface with opto–isolation. The energy to power
the LED in the TXD channel and to provide the positive voltage for the host’s RXD input is stolen from
DTR and RTS. The negative voltage for the RXD input is taken from the TXD line through a parasitic
supply consisting of a Schottky diode in series with a capacitor. The HCPL–2202 opto–isolator has a
totem pole output that allows switching in positive as well as negative voltage. The +5V are sufficient for
most RS232C systems. Switching in 12V requires an opto–isolator with different voltage characteristics.
In the schematic the HCPL–2202 opto–isolator is sourced by the RXD pin of the DS2480B. It can as well
be connected the traditional way where the DS2480B sinks the current through the LED. This, however,
causes a signal inversion that has to be compensated through the DS2480B by using a value code of 100,
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101, 110 or 111 for the RS232 baud rate setting. Using other types of opto–isolators than shown in the
schematic will at least require changing the values of the resistors.
RS232 DATA TIMING RXD LINE Figure 11
RECEIVE DELAY TIMING Figure 12
RS232 DATA TIMING TXD LINE Figure 13
TXD LINE ASYMMETRY Figure 14
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FUNCTION AND SPEED MATRIX Table 7
Baud Rate
9600 bps
19200 bps
57600 bps
115200 bps
v
X
Regular
v
v
X
v
X
X
X
X
1-Wire Speed
Flexible
v
v
X
X
X
X
X
X
Overdrive
v
v
v
v
v
v
X
v
Function
Search
Command/Data
Search
Command/Data
Search
Command/Data
Search
Command/Data
tIDLET is guaranteed by the UART; no precautions necessary
not recommended unless tIDLET is controlled by the host through a wait function
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ABSOLUTE MAXIMUM RATINGS*
Voltage on 1-W to Ground
Voltage on RXD, TXD, POL to Ground
Operating Temperature
Storage Temperature
Soldering Temperature
–0.5V to +14.0V
–0.5V to +7.0V
–40°C to +85°C
–55°C to +125°C
260°C for 10 seconds
* 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.
DC ELECTRICAL CHARACTERISTICS
PARAMETER
Supply Voltage
Programming Voltage
Operating Current
Idle Current on VPP
Active Pullup Timer Threshold
Active Pullup On Threshold
1-Wire Input High
1-Wire Input Low
TXD/POL Input Resistor
TXD/POL Input Levels
TXD/POL Input Levels
1-Wire Weak Pullup Current
1-Wire Active Pullup Current
Strong Pullup Voltage Drop
@ 10 mA load on 1-W
Programming Voltage Drop
@ 10 mA load on 1-W
RXD Sink Current @ 0.4V
RXD Source Current @ VDD-0.4V
Power On Reset Trip Point
VPP Sensor Trip Point
SYMBOL
VCC
VPP
IDD
IPP
VIAPTO
VIAPO
VIH1
VIL1
RI
VIH
VIL
IWEAKPU
IACTPU
∆VSTRPU
(VDD=4.5V to 5.5V; -40°C to 85°C)
MIN
4.5
VDD-1.4
TYP
5.0
12.0
3.0
20
VDD-1.1
0.95
NOTES
0.6
UNITS
V
V
mA
µA
V
V
V
V
kΩ
V
V
mA
mA
V
0.30
V
5
1.2
3.4
1.8
30
2.7
1.5
9
3.0
15
∆VPROG
IOLR
IOHR
VPOR
VPPTRIP
MAX
5.5
12.25
5.0
0.8
5.0
6
-4
3.3
9.5
CAPACITANCES
PARAMETER
TXD/POL Input Capacitance
1-Wire Input Capacitance
1
2
15
3
15
4
mA
mA
V
V
(tA = 25°C)
SYMBOL
CIN
CIN1
MIN
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TYP
5
10
MAX
UNITS
pF
pF
NOTES
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DS2480B
AC ELECTRICAL CHARACTERISTICS
PARAMETER
UART Bit Time
Device Bit Time
Fall Time RXD
Rise Time RXD
Transmit Idle Time
Receive Idle Time
Asymmetry
Arrival Response Time
Master Reset Time
Active Pull-Up on Time
Response Time
SYMBOL
TT
TR
tFR
tRR
tIDLET
tIDLER
tASYM
tARR
tMR
tAPUOT
tRESP
(VDD=4.5V to 5.5V; -40°C to 85°C)
MIN
8.68
8.68
8
13
0
TYP
MAX
104
104
20
27
tIDLET
4.4
104
0.5
8.68 + ∆
1
52
2.0
104 + ∆
UNITS
µs
µs
ns
ns
µs
µs
µs
µs
µs
µs
µs
NOTES
6
6, 7
8
8
9
10
11
12
13
11, 14
NOTES:
1. VPP– ∆VPROG must be within 11.5 to 12.0V.
2. Applies only if a 12.0V supply is connected. If VPP and VDD are tied together, current is less than
1 µA.
3. Input load is to GND.
4. Voltage difference between VDD and 1–W.
5. Voltage difference between VPP and 1–W.
6. 8.68 µs (115.2 kbps), 52 µs (19.2 kbps), 17.36 µs (57.6 kbps), 104 µs (9.6 kbps).
7. Nominal values; tolerance = ±5%.
8. At VCC = 5.0V and 100 pF load to GND.
9. See Table 7, Function and Speed Matrix.
10. Independent of baud rate.
11. Minimum at 115.2 kbps, maximum at 9.6 kbps.
12. The master reset cycle is complete after tMR is over.
13. Minimum value at Overdrive speed; maximum value at regular speed.
14. ∆ is the time to complete the activity on the 1–Wire bus; values range from 0 (configuration
command) up to 5130 µs (alarming presence pulse).
15. With regular and flexible speed the total capacitive load of the 1-Wire bus should not exceed 20 nF,
otherwise the active pullup on threshold VIAPO may not be reached in the available time. With
Overdrive speed the capacitive load on the 1-Wire bus must not exceed 1 nF.
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