DS1921H/Z Maxim Integrated Products, DS1921H/Z Datasheet - Page 23

• Manufacturer Part Number: DS1921H/Z
• Description: High Resolution Thermochron Ibutton Range H
• Manufacturer: Maxim Integrated Products

in Overdrive. The value of the pull-up resistor primarily depends on the network size and load conditions.
For most applications the optimal value of the pull-up resistor will be approximately 2.2kW.
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. With the DS1921H/Z the bus must be left low for no longer than 15.2µs at Overdrive
speed to ensure that none of the slave devices on the 1-Wire bus performs a reset. Despite of its limited
compliance, the DS1921H/Z will communicate properly when used in conjunction with a DS2480B 1-
Wire driver and serial port adapters that are based on this driver chip.
HARDWARE CONFIGURATION Figure 11
TRANSACTION SEQUENCE
The protocol for accessing the DS1921H/Z via the 1-Wire port is as follows:
§ Initialization
§ ROM Function Command
§ Memory Function Command
§ Transaction/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 presence pulse(s) transmitted by the
slave(s).
The presence pulse lets the bus master know that the DS1921H/Z is on the bus and is ready to operate.
For more details, see the 1-Wire Signaling section.
ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the seven ROM function commands. All
ROM function commands are eight bits long. A list of these commands follows (refer to flowchart in
Figure 12).
RX
TX
BUS MASTER
Open Drain
Port Pin
V
PUP
SEE
TEXT
RX = RECEIVE
TX = TRANSMIT
23 of 40
5µA
Typ.
DATA
DS1921 1-Wire PORT
100 W
MOSFET
RX
TX