DS2405 Datasheet by Maxim Integrated

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1 of 15 071107
FEATURES
Open-drain PIO pin is controlled by
matching 64-bit, laser-engraved registration
number associated with each device
Logic level of open drain output can be
determined over 1-Wire® bus for closed-loop
control
PIO pin sink capability is greater than 4mA
at 0.4V
Multiple DS2405s can be identified on a
common 1-Wire bus and be turned on or off
independent of other devices on the bus
Unique, factory-lasered and tested 64-bit
registration number (8-bit family code +48-
bit serial number +8-bit CRC tester) assures
absolute identity because no two parts are
alike
Built-in multidrop controller ensures
compatibility with other MicroLAN products
Reduces control, address, data, and power to
a single data pin
Directly connects to a single port pin of a
microprocessor and communicates at up to
16.3kbits/s
8-bit family code specifies DS2405
communications requirements to reader
8-bit cyclic redundancy check ensures error-
free selection
Zero standby power required
Low cost TO-92, SOT-223, or 6-pin TSOC
surface mount package
1-Wire communication operates over a wide
voltage range of 2.8V to 6.0V from -40°C to
+85°C
PIN ASSIGNMENT
TSOC PACKAGE
NOTE: The leads of TO-92 packages on tape-and-reel are
formed to approximately 100 mils (2.54 mm) spacing. For
details refer to drawing 56-G0006-003.
PIN DESCRIPTION TSOC
Pin 1 - Ground Pin 1 - Ground
Pin 2 - Data Pin 2 - Data
Pin 3 - PIO Pin 3 - PIO
Pin 4 - Ground Pin 4-6 -No Connect
DS2405
A
ddressable Switch
www.maxim-ic.com
TOP VIEW
TOP VIEW
3.7 X 4.0 X 1.5
GND
DAT
A
PIO
N
C
N
C
N
C
BOTTOM VIEW
See Mech.
Drawings Section
TO-92
DS2405
2 3
1
1 2 3
1-Wire is a registered trademark of Dallas Semiconductor.
DS2405
2 of 15
ORDERING INFORMATION
DS2405 TO-92 package
DS2405Z 4-pin SOT-223 package
DS2405P 6-pin TSOC package
DS2405/T&R Tape & Reel version of DS2405
DS2405Z/T&R Tape & Reel version of DS2405Z
DS2405P/T&R Tape & Reel version of DS2405P
DESCRIPTION
The DS2405 Addressable Switch is an open drain N-channel transistor that can be turned on or off by
matching the 64-bit factory-lasered registration number within each part. The 64-bit number consists of
an 8-bit family code, a unique 48-bit serial number, and an 8-bit cyclic redundancy check.
Communication with the DS2405 follows the standard Dallas Semiconductor 1-Wire protocol and can be
accomplished with a single port pin of a microcontroller. Multiple DS2405 devices can reside on a
common 1-Wire bus creating a MicroLAN. The network controller circuitry is embedded within the chip
including a search algorithm to determine the identity of each DS2405 on the network. The open drain
output (PIO pin) for each DS2405 on the MicroLan can be independently toggled on or off whether there
is one or many devices sharing the same 1-Wire bus. The logic level of the PIO pin for each device on the
MicroLan can also be individually sensed and reported to the bus master.
OVERVIEW
The DS2405 Addressable Switch provides a means for assigning an electronically readable identification
to a particular node or location with additional control capability provided by an open drain N-channel
MOSFET that can be remotely switched and sensed via communication over the 1-Wire bus. The DS2405
contains a factory-lasered registration number that includes a unique 48-bit serial number, an 8-bit CRC,
and an 8-bit family code (05h). The 64-bit ROM portion of the DS2405 not only creates an absolutely
unique electronic identification for the device itself but also is a means to locate and change or obtain the
state of the switch that is associated with the 64-bit ROM. The structure of the 64-bit ROM is shown in
Figure 1. The device derives its power entirely from the 1-Wire bus by storing energy on an internal
capacitor during periods of time when the signal line is high and continues to operate off of this “parasite”
power source during the low times of the 1-Wire line until it returns high to replenish the parasite
(capacitor) supply. The DS2405 uses the standard Dallas Semiconductor 1-Wire protocol for data
transfers, with all data being read and written least significant bit first. Communication to and from the
DS2405 requires a single bidirectional line that is typically the port pin of the microcontroller. The 1-
Wire bus master (microcontroller) must first issue one of five ROM function commands: 1) Read ROM,
2) Match ROM, 3) Search ROM, 4) Skip ROM, and 5) Active-Only Search ROM. These commands
operate on the 64-bit lasered ROM portion of each device and can singulate a specific device if many are
present on the 1-Wire line as well as indicate to the bus how many and what type of each device is
present. The protocol required for these ROM function commands is described in Figure 4. After a ROM
function command is successfully executed, the open drain output can be toggled or its current status
determined via the 1-Wire bus.
1-WIRE BUS SYSTEM
The 1-Wire bus is a system that has a single bus master and one or more slaves. In all instances, the
DS2405 is a slave device. The bus master is typically a microcontroller. The discussion of this bus system
is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling
(signal type and timing). For a more detailed protocol description, refer to Chapter 4 of the Book of
DS19xx iButton® Standards.
DS2405
3 of 15
Hardware Configuration
The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to
drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have an
open drain connection or 3-state outputs. The DS2405 is an open drain part with an internal circuit
equivalent to that shown in Figure 2. The bus master can be the same equivalent circuit. If a bidirectional
pin is not available, separate output and input pins can be tied together. The bus master requires a pullup
resistor at the master end of the bus, with the bus master circuit equivalent to the one shown in Figure 3.
The value of the pullup resistor should be approximately 5 kΩ for short line lengths. A multidrop bus
consists of a 1-Wire bus with multiple slaves attached. The 1-Wire bus has a maximum data rate of
16.3kbits/s.
The idle state for the 1-Wire bus is high. If, for any reason, a transaction needs to be suspended, the bus
MUST be left in the idle state if the transaction is to resume. If this does not occur and the bus is left low
for more than 120 μs, one or more of the devices on the bus may be reset. In addition, the state of the PIO
pin for one or more of the DS2405s on the bus may return to its default (off) condition.
DS2405 MEMORY MAP Figure 1
8-Bit CRC Code 48-Bit Serial Number 8-Bit Family Code (05h)
MSB LSB MSB LSB MSB LSB
DS2405 EQUIVALENT CIRCUIT Figure 2
Vnn BUS MASTER 055000 on 3051 EQUIVMENT Oven Dram PM Pin H T E VDD % 5m $ B) VDD BUS MASTER TfLrEquivalem Pm wins Vun 5m 5m
DS2405
4 of 15
BUS MASTER CIRCUIT Figure 3
A) Open Drain
TRANSACTION SEQUENCE
The sequence for accessing the DS2405 via the 1-Wire port is as follows:
Initialization
ROM Function Command
Read Data
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence
consists of a Reset Pulse transmitted by the bus master followed by a Presence Pulse(s) transmitted by the
slave(s).
The Presence Pulse lets the bus master know that at least one DS2405 is on the bus and is ready to
operate. For more details, see the “1-Wire Signaling” section.
B
)
Standard TTL
To data connection
of DS2405
To data connection
of DS2405
DS2405
5 of 15
ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of five ROM function commands. All ROM
function commands are 8 bits long. A list of these commands follows (refer to flowchart in Figure 4).
Read ROM [33h]
This command allows the bus master to read the DS2405’s 8-bit family code, unique 48-bit serial
number, and 8-bit CRC. This command can be used only if there is a single DS2405 on the bus. If more
than one slave is present on the bus, a data collision will occur when all slaves try to transmit at the same
time (open drain will produce a wired-AND result).
Match ROM [55h]
The Match ROM command, followed by a 64-bit ROM sequence, allows the bus master to address a
specific device on a multidrop bus. All devices that do not match the 64-bit ROM sequence will wait for a
Reset Pulse. The DS2405 that exactly matches the 64-bit ROM sequence will toggle the state of its PIO
pin after the 64th bit of the match is entered. If the open drain N-channel device was off, it will be turned
on and vice versa. After the last bit of the ROM sequence is received from the bus master and the PIO pin
of the selected DS2405 has toggled, additional read time slots issued by the bus master will cause the
DS2405 to output the logic state of its PIO pin onto the 1-Wire bus. If the pulldown is on and the PIO pin
is a logical 0, the DS2405 will respond with read-0 time slots. If the pulldown is off and the PIO pin is a
logical 1 (external pullup is required), the DS2405 will respond with read-1 time slot. Each additional
read time slot issued by the bus master will continue to indicate the state of the PIO pin until a Reset
Pulse is received from the bus master.
Search ROM [F0h]
When a system is initially interrogated, the bus master may not know the number of devices on the 1-
Wire bus or their 64-bit ROM codes. The Search ROM command allows the bus master to use a process
of elimination to identify the 64-bit ROM codes of all slave devices on the bus. This process of
elimination involves repeated application of a simple three-step procedure where the bus master starts by
reading a bit position in the 64-bit ROM, followed by reading the complement of that bit position, and
finally writing to all the devices still involved in the search the desired logic value for that bit position. An
example is shown below and a flowchart for the search algorithm can be found in the “Book of DS19xx
iButton Standards.”
Four devices are connected to the 1-Wire bus. Their binary ROM contents are listed below:
device 1: xxxxxx10101100
device 2: xxxxxx01010101
device 3: xxxxxx10101111
device 4: xxxxxx10001000
The x’s represent the higher remaining bits. Shown are the lowest 8 bits of the ROM contents. The least
significant bit is to the right in this representation. The search process runs as follows:
1. The master begins the initialization sequence by issuing a Reset Pulse. The devices respond by issuing
Presence Pulses.
2. The master will then issue the Search ROM command on the 1-Wire bus.
DS2405
6 of 15
3. The master reads 1 bit from the 1-Wire bus. Each device will respond by placing the value of the first
bit of its respective ROM data onto the 1-Wire bus. Devices 1 and 4 will place a 0 onto the 1-Wire
bus; that is, they pull it low. Devices 2 and 3 will send a 1 by allowing the line to stay high. The result
is the logical AND of all devices on the line; therefore the master reads a 0. The master will issue
another read time slot. Since the ROM Search command is being executed, all devices respond to this
second read by placing the complement of the first bit of their respective ROM data onto the 1-Wire
Bus. Devices 1 and 4 will send a 1; devices 2 and 3 will send a 0. Thus the 1-Wire bus will be pulled
low. The master again reads a 0 for the complement of the first ROM data bit. This tells the master
that there are devices on the bus that have a 0 in the first position and others that have a 1. If all
devices had a 0 in this bit position, the reading would be 01; if the bit position contained a 1, the result
would be 10. (Note that the 11 condition indicates that no devices are present on the 1-Wire bus.)
4. The master now decides to write a 0 on the 1-Wire bus. This deselects Devices 2 and 3 for the
remainder of the search pass, leaving only devices 1 and 4 participating in the search process.
5. The master performs two more reads and receives a 0 followed by a 1 bit. This indicates that all active
devices have a 0 in this bit position of their ROM.
6. The master then writes a 0 to keep devices 1 and 4 selected.
7. The master executes two reads and receives two 0 bits. This again indicates that both 1 and 0 exist as
the third bit of the ROM of the active devices.
8. The master again writes a 0. This deselects device 1, leaving device 4 as the only active device.
9. Subsequent reads to the end of the ROM will not show bit conflicts. Therefore, they directly tell the
master the ROM contents of the active device. After having learned any new ROM bit, the master has
to resend this bit to keep the device selected. As soon as all ROM bits of the device are known and the
last bit is resent by the master, the device is ready to output the state of the PIO pin using additional
read time slots.
10. The master must learn the other devices’ ROM data. Therefore, it starts another ROM Search
sequence by repeating steps 1 through 7.
11. At the highest bit position, where the master wrote a 0 at the first pass (step 8), it now writes a 1. This
deselects device 4, leaving device 1 active.
12. As in step 9, subsequent reads to the end of the ROM will not show bit conflicts. This completes the
second ROM Search pass where the master has learned another ROM’s contents.
13. The master must learn the other devices’ ROM data. Therefore, it starts another ROM Search
sequence by repeating steps 1 to 3.
14. At the second highest bit position where the master wrote a 0 at the first pass (step 4), it now writes a
1. This deselects devices 1 and 4, leaving devices 2 and 3 active.
15. The master sends two read time slots and receives two 0 bits, indicating a bit conflict.
16. The master again decides to write a 0. This deselects device 3, leaving device 2 as the only active
device.
17. As in step 9, subsequent reads to the end of the ROM will not show bit conflicts. This completes the
third ROM Search pass where the master has learned another ROM’s contents.
DS2405
7 of 15
18. The master must learn the other devices’ ROM data. Therefore it starts another ROM Search sequence
by repeating steps 13 to 15.
19. At the highest bit position where the master wrote a 0 at the previous pass (step 16), it now writes a 1.
This deselects device 2, leaving device 3 active.
20. As in step 17, subsequent reads to the end of the ROM will not show bit conflicts. This completes the
fourth ROM Search pass where the master has learned another ROM’s contents.
After one complete pass, the bus master knows the contents of the 64-bit ROM in one device. Subsequent
passes will reveal the total number of devices and their individual ROM codes. In addition, after each
complete pass of the search that successfully determines the 64-bit ROM for a specific device on the
multidrop bus, that particular device can be individually accessed as if a Match ROM has been issued
since all other devices will have dropped out of the search process and are waiting for a Reset Pulse. The
DS2405 that was discovered by the search process will not toggle the state of its PIO pin at the end of the
search, but additional read time slots issued by the bus master after the search is completed will cause the
DS2405 to output the logic state of its PIO pin onto the 1-Wire bus. If the pulldown is on and the PIO pin
is a logical 0, the DS2405 will respond with read-0 time slots. If the pulldown is off and the PIO pin is a
logical 1 (external pullup is required), the DS2405 will respond with read-1 time slots. Each additional
read time slot issued by the bus master will continue to indicate the state of the PIO pin until a Reset
Pulse is received from the bus master. The combination of Match ROM and Search ROM allows the user
to change the state of the PIO pin and report the current state (Match ROM) or simply report the current
state of the PIO pin without changing it (Search ROM).
Active-Only Search ROM [ECh]
The Active-Only Search ROM command operates similarly to the Search ROM command except that
only devices with their output pulldown turned on are allowed to participate in the search. This provides
an efficient means for the bus master to determine devices on a multidrop system that are active (PIO pin
driven low). After each pass of the active-only search that successfully determines the 64-bit ROM for a
specific device on the multidrop bus with its output pulldown turned on, that particular device can be
individually accessed as if a Match ROM had been issued since all other devices will have dropped out of
the active-only search process and are waiting for a Reset Pulse. The DS2405 that was discovered by the
active-only search process will not toggle the state of its PIO pin at the end of the search, but additional
read time slots issued by the bus master after the search is completed will cause the DS2405 to output the
logic state of the PIO pin (see Figure 2) onto the 1-wire bus. Since the Active-Only Search ROM
command only operates on devices with their pulldown on, the internal CONTROL signal for each of
these parts is always a logical 1. With CONTROL=1, the selected DS2405 will respond to the bus master
with read-0 time slots after an active-only search pass is successfully completed. Each additional read
time slot issued by the bus master will continue to appear as a read-0 until a Reset Pulse is received from
the bus master. If the CONTROL signal is a logical 0 for any DS2405, that device will not participate in
the Active-Only Search. The combination of Search ROM and Active-Only Search ROM allows the user
to search in the most efficient manner depending on the requirements. If the bus master interrogates a
multidrop system comprised of DS2405s whose PIO conditions are unknown, the Active-Only Search
can quickly determine which devices are turned on. The two commands also allow the bus master to
separately determine the state of the PIO pin and the internal CONTROL signal which may be useful in
detecting certain conditions. If Search ROM returns read-0 time slots (PIO=logical 0) for a given device,
it may be due to that particular DS2405 driving its PIO pin low, or under certain conditions the logical 0
may be caused by some other device holding PIO low. If that same device is found using an active-only
search, CONTROL must be a logical 1 and the PIO pin is being held low by the DS2405. If that same
DS2405
8 of 15
device is not found using an active-only search, CONTROL must be a logical 0 and the PIO pin is being
held low by some other device or perhaps a fault condition such as a PIO shorted to ground. A second
fault condition may be detected if Search ROM for a given device returns read-1 time slots (PIO=logical
1) but Active-Only Search ROM is successful (CONTROL=logical 1) and returns read-0 time slots for
the same device, indicating the possibility that PIO may be shorted to a positive voltage.
032405 TX FAMLY CODE I 5er D32405 TX cRc 5st 052405 T)( rs MASTER Tx REsET PULSE I 052405 Tx PRESENCE PULSE FROM FIGURE A SECOND PART I MASTER TX RoM FUNCTION COMMAND 55h MATCH RoM COMMAND MASTER Tx BIT o MASTER TK BIT I v N T MASTER Tx BIT as err 53 MATCH7 MASTER TX REsET To FIGURE A, SECOND PART Eon SEARCH RoM COMMAND N D52405 TX BIT u Dszws Tx B111 MASTER Tx an o N am: MATCH? v uszws Tx BIT I DSZADS Tx EI'I'T MASTER TX BIT I V'r DSZAOS Tx BIT In nsms TX m MASTER TX BIT 53 Dszms TDGGLES PIO RIN MASTER Tx RESET 7 DsaAas TX 0's 052405 TK D's N usons Tx 1's
DS2405
9 of 15
ROM FUNCTIONS FLOW CHART Figure 4
TO HGURE A, HRST PARY F FVGUHE 4, "SHST PART 052405 1x an o DSZJDS Tx m MASTER Tx an o 052405 rx 1's N BIT o MATCH? v 052405 1x BIT ‘ 052405 TX EITT MASTER TX E|T\ VT Dszms TX Err 53 052405 TX arr 5: MASTER Tx BIT 53 032405 Tx D’S
DS2405
10 of 15
ROM FUNCTIONS FLOW CHART Figure 4 (cont.)
MASTER TX “RESET PULSE" MASTER Rx "PRESENCE PULSE" ‘ <___j~ ‘—="" ‘rsth="" vpullup="" —~="" vpulvip="" min="" ih="" min="" vil="" max="" '="" 0v=""><——- tr511.="" -———=""> ‘* 1PDH ‘— .\ E' §V
DS2405
11 of 15
Skip ROM [CCh]
The complete 1-Wire protocol for all Dallas Semiconductor iButtons contains a Skip ROM command.
Since the DS2405 contains only the 64-bit ROM with no additional data fields, the Skip ROM is not
applicable and will cause no further activity on the 1-Wire bus if executed. The DS2405 does not interfere
with other 1-Wire parts on a multidrop bus that do respond to a Skip ROM (for example, a DS2405 and
DS1994 on the same bus).
1-WIRE SIGNALING
The DS2405 requires strict protocols to ensure data integrity. The protocol consists of four types of
signaling on one line: reset sequence with Reset Pulse and Presence Pulse, write 0, write 1 and read data.
All these signals except Presence Pulse are initiated by the bus master.
The initialization sequence required to begin any communication with the DS2405 is shown in Figure 5.
A Reset Pulse followed by a Presence Pulse indicates the DS2405 is ready to send or receive data given
the correct ROM command.
The bus master transmits (TX) a Reset Pulse (tRSTL, minimum 480μs). The bus master then releases the
line and goes into receive mode (RX). The 1-Wire bus is pulled to a high state via the 5kΩ pullup resistor.
After detecting the rising edge on the data pin, the DS2405 waits (tPDH, 15-60μs) and then transmits the
Presence Pulse (tPDL, 60-240μs).
INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” Figure 5
480μs tRSTL < *
480μs tRSTH < (includes recovery time)
15μs tPDH < 60μs
60μs tPDL < 240μs
In order not to mask interrupt signaling by other devices on the 1-Wire bus, tRSTL + tR should always
be less than 960μs.
RESISTOR
MASTER
DS2405
A© tSLOT V VPULLUP PULLUP MIN V . m Mm 032405 VIL MAX 7 SAMPLING WINDOW 0V Q§® v [A Q®® ‘HEC ‘SLOT VFULLUP V \ PUL‘VU: mm ‘\ 952405 \ V"_ MAX SAMPLING WINDOW \ CV 15 E ‘— so us _. ‘ ‘Lowo , W
DS2405
12 of 15
READ/WRITE TIME SLOTS
The definitions of write and read time slots are illustrated in Figure 6. All time slots are initiated by the
master driving the data line low. The falling edge of the data line synchronizes the DS2405 to the master
by triggering a delay circuit in the DS2405. During write time slots, the delay circuit determines when the
DS2405 will sample the data line. For a read data time slot, if a “0” is to be transmitted, the delay circuit
determines how long the DS2405 will hold the data line low overriding the “1” generated by the master.
If the data bit is a 1, the device will leave the read data time slot unchanged.
READ/WRITE TIMING DIAGRAM Figure 6
Write-1 Time Slot
60μs tSLOT < 120μs
1μs tLOW1 < 15μs
1μs tREC <
Write-0 Time Slot
60μs tLOW0 < tSLOT < 120μs
1μs tREC <
RESISTOR
MASTER
ununun MIN
DS2405
13 of 15
READ/WRITE TIMING DIAGRAM Figure 6 (cont.)
Read-Data Time Slot
60μs tSLOT < 120μs
1μs tLOWR < 15μs
0 tRELEASE < 45μs
1μs tREC <
tRDV = 15μs
tSU < 1μs
CRC GENERATION
To validate the data transmitted from the DS2405, the bus master may generate a CRC value from the
data as it is received. This generated value is compared to the value stored in the last 8 bits of the
DS2405. If the two CRC values match, the transmission is error-free.
The equivalent polynomial function of this CRC is:
CRC = x8 + x5 + x4 + 1
For more details, see the Book of DS19xx iButton Standards.
RESISTOR
MASTER
DS2405
VPUP % @ VPUP
DS2405
14 of 15
ABSOLUTE MAXIMUM RATINGS*
Voltage on any Pin Relative to Ground -0.5V to +7.0V
Operating Temperature Range -40°C to +85°C
Storage Temperature Range -55°C to +125°C
Solder Temperature See J-STD-020A Specification
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 (-40°C to +85°C; VPUP = 2.8V to 6.0V)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Logic 1 VIH 2.2 VCC +0.3 V 1,6,8
Logic 0 VIL -0.3 +0.8 V 1,10
Output Logic Low @ 4 mA VOL 0.4 V 1
Output Logic High VOH V
PUP 6.0 V 1,2
Input Load Current (DATA pin) IL 5
μA 3
Input Resistance (PIO pin) IR 10 MΩ 9
CAPACITANCE (tA = 25°C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Capacitance DATA pin CD 800 pF 7
Capacitance PIO pin CP 10 pF
AC ELECTRICAL CHARACTERISTICS (-40°C to +85°C; VPUP =2.8V to 6.0V)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Time Slot tSLOT 60 120 μs
Write-1 Low Time tLOW1 1 15 μs 12
Write-0 Low Time tLOW0 60 120 μs
Read Low Time tLOWR 1 15 μs 12
Read Data Valid tRDV 15 μs 11
Release Time tRELEASE 0 15 45 μs
Read Data Setup tSU 1
μs 5
Recovery Time tREC 1 μs
Reset Time High tRSTH 480 μs 4
Reset Time Low tRSTL 480 960 μs 13
Presence Detect High tPDH 15 60 μs
Presence Detect Low tPDL 60 240 μs
DS2405
15 of 15
NOTES:
1. All voltages are referenced to ground.
2. VPUP = external pullup voltage.
3. Input load is to ground.
4. An additional reset or communication sequence cannot begin until the reset high time has expired.
5. Read data setup time refers to the time the host must pull the 1-Wire bus low to read a bit. Data is
guaranteed to be valid within 1μs of this falling edge and will remain valid for 14μs minimum (15μs
total from falling edge on 1-Wire bus).
6. VIH is a function of the external pull-up resistor and the VCC supply.
7. Capacitance on the data pin could be 800pF when power is first applied. If a 5kΩ resistor is used to
pull-up the data line to VCC, 5μs after power has been applied the parasite capacitance will not affect
normal communications.
8. VIH for PIO pin should always be greater than or equal to VPUP -0.3V.
9. Input resistance is to ground.
10. Under certain low voltage conditions VILMAX may have to be reduced to as much as 0.5V to always
guarantee a Presence Pulse.
11. The optimal sampling point for the master is as close as possible to the end of the 15μs tRDV period
without exceeding tRDV. For the case of a Read 1 time slot, this maximizes the amount of time for the
pull-up resistor to recover the line to a high level. For a Read 0 time slot, it ensures that a read will
occur before the fastest 1-Wire device(s) release the line.
12. The duration of the low pulse sent by the master should be a minimum of 1μs with a maximum value
as short as possible to allow time for the pull-up resistor to recover the line to a high level before the
1-Wire device samples in the case of a Write 1 Low Time, or before the master samples in the case of
a Read Low Time.
13. The Reset Low Time (tRSTL) should be restricted to a maximum of 960μs to allow interrupt signaling;
otherwise, it could mask or conceal interrupt pulses.

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