DS1922T-F5 MAXIM [Maxim Integrated Products], DS1922T-F5 Datasheet - Page 35

• Manufacturer Part Number: DS1922T-F5
• Description: Temperature Logger iButton With 8kB Datalog Memory
• Manufacturer: MAXIM [Maxim Integrated Products]

1-Wire protocol defines bus transactions in terms of the bus state during specific time slots that are initiated on the
falling edge of sync pulses from the bus master. For a more detailed protocol description, refer to Chapter 4 of the
Book of DS19xx iButton Standards.
HARDWARE CONFIGURATION
The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to drive it at
the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have open drain or tri-state
outputs. The 1-Wire port of the DS1922L/T is open-drain with an internal circuit equivalent to that shown in Figure
10.
A multidrop bus consists of a 1-Wire bus with multiple slaves attached. At standard speed the 1-Wire bus has a
maximum data rate of 16.3kbps. The speed can be boosted to 142kbps by activating the Overdrive mode. The
DS1922L/T is not guaranteed to be fully compliant to the iButton standard. Its maximum data rate in standard
speed mode is 15.4kbps and 125kbps in Overdrive. The value of the pullup resistor primarily depends on the
network size and load conditions. The DS1922L/T requires a pullup resistor of maximum 2.2kΩ at any speed.
The idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus MUST be
left in the idle state if the transaction is to resume. If this does not occur and the bus is left low for more than 16µs
(Overdrive speed) or more than 120µs (standard speed), one or more devices on the bus may be reset. Note that
the DS1922L/T does not quite meet the full 16µs maximum low time of the normal 1-Wire bus Overdrive timing.
With the DS1922L/T the bus must be left low for no longer than 12µs at Overdrive to ensure that no DS1922L/T on
the 1-Wire bus performs a reset. The DS1922L/T communicates properly when used in conjunction with a
DS2480B or DS2490 1-Wire driver and adapters that are based on these driver chips.
Figure 10. Hardware Configuration
TRANSACTION SEQUENCE
The protocol for accessing the DS1922L/T through the 1-Wire port is as follows:
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a
reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the slave(s). The presence
pulse lets the bus master know that the DS1922L/T is on the bus and is ready to operate. For more details, see the
1-Wire Signaling section.
Initialization
ROM Function Command
Memory/Control Function Command
Transaction/Data
RX
TX
BUS MASTER
Open-Drain
Port Pin
V
PUP
R
RX = RECEIVE
TX = TRANSMIT
PUP
35 of 50
5µA
Typ.
DATA
DS1922L/T 1-Wire PORT
100Ω
MOSFET
DS1922L/DS1922T
RX
TX