DS2480 ,Serial 1-Wire Line DriverPIN DESCRIPTIONfor serial and 1-Wire communicationGND GroundSlew rate controlled 1-Wire pull-down a ..
DS2480B ,Serial 1-Wire Line Driver with Load Sensorblock diagram (see Figure 1). The device gets its input data from the serial communication port of ..
DS2480B ,Serial 1-Wire Line Driver with Load SensorPIN DESCRIPTION (default), 19.2kbps, 57.6kbps, and 115.2kbps GND - Ground o Self-Calibrating Ti ..
DS2480B+ ,Serial to 1-Wire Line DriverPIN DESCRIPTION (default), 19.2kbps, 57.6kbps, and 115.2kbps GND - Ground o Self-Calibrating Ti ..
DS2480B+T , Serial to 1-Wire Line Driver
DS2480S ,Serial 1-Wire Line DriverPIN DESCRIPTIONPIN SYMBOL DESCRIPTION1 GND Ground Pin: common ground reference and ground return fo ..
E53NA50 ,NABSOLUTE MAXIMUM RATINGSSymbol Parameter Value UnitV Drain-source Voltage (V =0) 500 VDS GSV 500 VD ..
EA2-12 ,COMPACT AND LIGHTWEIGHTAPPLICATIONSElectronic switching systems, PBX, key telephone systems, automatic test equipment and ..
EA2-12NU ,COMPACT AND LIGHTWEIGHTFEATURESª Low power consumptionª Compact and light weightª 2 form c contact arrangementª Low magnet ..
EA2-12S ,COMPACT AND LIGHTWEIGHTFEATURESª Low power consumptionª Compact and light weightª 2 form c contact arrangementª Low magnet ..
EA2-12TNU ,COMPACT AND LIGHTWEIGHTAPPLICATIONSElectronic switching systems, PBX, key telephone systems, automatic test equipment and ..
EA2-4.5NU ,COMPACT AND LIGHTWEIGHTAPPLICATIONSElectronic switching systems, PBX, key telephone systems, automatic test equipment and ..
DS2480
Serial 1-Wire Line Driver
FEATURESUniversal, common-ground serial port to
1-WireTM line driver for MicroLANTM
applications
Works with all iButtons™ and MicroLAN-compatible 1-Wire slave devices
Communicates at regular and Overdrive 1-Wire
speed and serial port data rates of 9600
(default), 19200, 57600 and 115200 bps
Supports 12V EPROM programming and stiff5V pull-up for Crypto iButton, sensors and
EEPROM
Self-calibrating time base with ±5% tolerance
for serial and 1-Wire communication
Slew rate controlled 1-Wire pull-down andactive pull-up 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 UARTsProgrammable 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 pinsCompatible to 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
PIN ASSIGNMENT
PIN DESCRIPTIONGNDGround
1-W1-Wire Input/OutputNo Connection
VDD4.5 to 5.5VVPPOptional EPROM
Programming Voltage
POLRXD/TXD Polarity Select
TXDSerial Data from UART
RXDSerial Data to UART
ORDERING INFORMATIONDS2480S8-pin SOIC
1-W
GND
8-PIN SOIC
(150 MIL)
VDD
DS2480
DS2480
DESCRIPTIONThe DS2480 is a serial port to 1-Wire interface chip that supports standard and Overdrive speeds. It
connects directly to UARTs and 5V RS232 systems. Interfacing to RS232C (± 12V levels) requires apassive 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 DS2480 can
translate each character into eight 1-Wire time slots thereby increasing the data throughput
significantly. In addition, the DS2480 can be set to communicate at four different data rates including115.2 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 DS2480 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 functionsof the DS2480 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
DS2480
OVERVIEWThe DS2480 directly interfaces a 5-volts 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 rateat the communication port to be different from the 1-Wire date 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 bymeans 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 thelogic level at POL specifies. As data enters the core of the DS2480’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 waveforms
on the 1-Wire bus. Command bytes either affect the configuration setting or generate certain waveformson 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 pull-up to 5-volts and
reads the 1-Wire bus using a non-TTL threshold to maximize the noise margin for best performance onlarge 1-Wire MicroLAN networks.
DS2480 BLOCK DIAGRAM FIGURE 1
DS2480
DEVICE OPERATIONThe DS2480 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 codesdetermine the behavior of the chip, as shown in the state transition diagram (Figure 2). The DS2480
requires and generates a communication protocol of 8 data bits per character, 1 stop bit and no parity. It is
permissible to use two stop bits on the TXD line. However, the DS2480 will only assert a single stop bit
on RXD. When powering up, the DS2480 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-Wirereset 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 DS2480 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. A master reset cycle can also be generated by means of software. This may be necessary if thehost for any reason has lost synchronization with the device. The DS2480 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 andselecting space polarity for the parity bit. As with the power-on reset, the DS2480 requires a 1-Wire reset
command sent by the host at a data rate of 9600 bps for calibration.
DS2480
STATE TRANSITION DIAGRAM Figure 2After the DS2480 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 statecalled Data Mode. In data mode the DS2480 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 Pull-up to 5-volts is enabled (see Pulse command) each byte
DS2480
While being in the Data Mode the DS2480 checks each byte received from the host for the reserved codethat 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 commandand 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 DS2480.
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 DS2480 has to be switched to Command mode. The host then sends theappropriate 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 DS2480 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
two bits marks the bus arrival. If the DS2480 is left in Data Mode after completing a memory functioncommand it will not report any bus arrival to the host.
COMMAND CODE OVERVIEWThe DS2480 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 theconfigurable 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 pull-up 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.In addition to the command codes explained in the subsequent sections the DS2480 understands the
following reserved command codes:
E1hswitch to Data Mode
E3hswitch to Command Mode
F1hpulse terminationExcept 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 E3hcommand while the Command Mode is still active.
COMMUNICATION COMMANDSThe DS2480 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 AcceleratorControl 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.
DS2480
COMMUNICATION COMMAND CODES TABLE 1
COMMUNICATION COMMAND RESPONSE TABLE 2(The Search Accelerator Control command does not generate a response byte.)
RESETThe 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 the1-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 BITThe 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 zero or write one) is determined by the logic value of bit 4. Aread data time slot is identical to the write one time slot. Bits 0 and 1 of the response byte transmitted by
the DS2480 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 pull-up bit 1 must be set to 1. As soon as the strong pull-up is over, the
device will send a second response byte, code EFh (read 1) or ECh (read 0), depending on the valuefound on the 1-Wire bus when reading. The strong pull-up directly following the single bit is used in
DS2480
SEARCH ACCELERATOR CONTROLThe 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 setto 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 pull-up 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.
PULSEThe Pulse command serves several functions that are selected by the contents of bit 1 and bit 4 of thecommand code. The main functions are generating a strong pull-up to 5-volts and generating 12-volts
programming pulses for EPROM devices (if the 12-volts are available at the VPP pin). The secondary
function of the pulse command is arming and disarming a strong pull-up after every subsequent byte in
data mode. The arm/disarm function is controlled by bit 1 of the command code. Bit 4 determines
whether the device will generate a strong pull-up to 5-volts or a 12-volts programming pulse. The tablebelow summarizes these options.
The strong pull-up to 5-volts 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 pull-up is disarmed most of the time. Although arming or disarming is simultaneously possiblewhile generating a programming pulse, this is not recommended since it is likely to destroy the DS2480 if
non-EPROM devices are connected to the 1-Wire bus. The duration of the strong pull-up or programming
pulse is determined by configuration parameters and ranges from a few microseconds up to unlimited (see
section Configuration Commands). However, unlimited duration is not allowed in conjunction with
arming the strong-pull-up after every byte. As long as the DS2480 is in Command Mode the host mayterminate a strong pull-up or programming pulse prematurely at any time by sending the command code
F1h. The response byte is generated as soon as the strong pull-up or programming pulse is over (either
because the predefined time has elapsed or due to termination). The response byte mainly returns the
command code as sent by the host, but the two least significant bits are undefined. If the strong pull-up is
armed and the device is in Data Mode, the end of the strong pull-up will be signaled as code F6h if themost significant bit of the preceding data byte on the 1-Wire bus was 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).
DS2480
SEARCH ACCELERATOR INTRODUCTIONThe Search Accelerator is a logic block inside the DS2480 that allows using the Search ROM function
very efficiently under modern operating systems such as Windows and Windows 95/NT. Without theDS2480 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 muchless 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
two 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 processtakes a 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.
The Search Accelerator receives from the host information on the preferred path to chose during theexecution of the Search ROM function 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 fora 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 wasdefined 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
DS2480 performs a Search ROM function.
SEARCH ACCELERATOR OPERATIONAfter the Search Accelerator is activated and the data mode is selected, the host must send 16 bytes tocomplete a single Search ROM pass on the 1-Wire bus. These bytes are constructed as follows:
first byte
et cetera
16th byte
DS2480
In this scheme, the index (values from 0 to 63, “n”) designates the position of the bit in the ROM ID of aMicroLAN 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 DS2480 will generate three time slots on the 1-Wire bus.
These are referenced as:b0for the first time slot (read data)for the second time slot (read data) andfor the third time slot (write data).
The type of time slot b2 (write 1 or write 0) is determined by the DS2480 as follows:= 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
et cetera
16th byte
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 positionand 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 1’s 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 re-uses 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 DS2480 to perform one pass
through the Search ROM function using the Search Accelerator. After a device has been identified and
addressed, a (not specified here) memory function is executed and finally a reset pulse is generated. This
example assumes that the DS2480 was in Command Mode and that regular 1-Wire speed is used.
DS2480
SEARCH ACCELERATOR USAGE EXAMPLE
CONFIGURATION COMMANDSThe DS2480 is designed to be configurable for the varying requirements of its application. When thedevice 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 DS2480 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 12-volts
programming pulse, the duration of the strong pull-up to 5-volts and the baud rate on the interface that
connects the DS2480 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) andadding 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 requireschanging 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 8 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.
DS2480
CONFIGURATION COMMAND OVERVIEW TABLE 3The numbers given for parameter 001 (Pull-Down Slew Rate Control) are nominal values. They may vary
as specified in the Electrical Characteristics section 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”.For the parameters 010 (Programming Pulse Duration) and 011 (Strong Pull-Up 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 pull-up) 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 DS2480 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. The parameter code
110 is reserved for future extensions; one should not change the value code from its default setting.
CONFIGURATION PARAMETER VALUE CODES Table 4
DS2480
The syntax of configuration commands is very simple. Each 8-bit code word contains a 3-bit parametercode 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 zeros 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. Whenreading 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 5BIT 5BIT 20
CONFIGURATION COMMAND RESPONSE BYTE Table 6BIT 5BIT 4BIT 2
CONTROLLED EDGESOne of the tasks of the DS2480 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 EDGESThe active pull-up of the rising edges reduces the rise time on the 1-Wire bus significantly compared to a
simple resistive pull-up. Figure 4 shows how the DS2480 is involved in shaping a rising edge.
ACTIVE PULL-UP Figure 4t2t3
VIAPTO
IS DISCHARGED
DS2480
The circuit operates as follows: At t1 the pull-down (induced by the DS2480 or a device on the bus) ends.From this point on the 1-Wire bus is pulled high by the weak pull-up current IWEAKPU provided by the
DS2480. The slope is determined by the load on the bus and the value of the pull-up current. At t2 the
voltage crosses the threshold voltage VIAPO. Now the DS2480 switches over from the weak pull-up
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 DS2480 will switch back
to the weak pull-up current.
FALLING EDGES (DS2480-INITIATED)Whenever the DS2480 begins pulling the 1-Wire bus low to initiate a time slot, for example, it first turns
off the weak pull-up current IWEAKPU. Then, at regular and Overdrive speed 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 forcommunication 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 DS2480-initiated falling edges. The effect of the slew rate control is shown in Figure 5.
SLEW RATE CONTROL Figure 5As 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 (Pull-Down 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 Pull-Down Slew Rate Control parameter should be stored in the
host and always be loaded into the DS2480 after apower-on or master reset cycle.
TIMING DIAGRAMSThis section explains the wave forms generated by the DS2480 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 DS2480 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.
0.8V
1-WIRE BUS
IS PULLED UP
WEAK PULL-UP ENDS,
PULL-DOWN BEGINSt1
