DS2703 Dallas Semiconductor, DS2703 Datasheet - Page 11

• Manufacturer Part Number: DS2703
• Description: SHA-1 Battery Pack Authentication IC
• Manufacturer: Dallas Semiconductor

HARDWARE CONFIGURATION
The DS2703 uses an open-drain output driver as part of the bidirectional interface circuitry shown in Figure 5. If a
bidirectional pin is not available on the bus master, separate output and input pins can be connected together. For
normal communication the 1-Wire bus must have a pullup resistor at the bus-master end of the bus. For short line
lengths and/or V
V
reason, a bus transaction must be suspended, the bus must be left in the idle state to properly resume the
transaction later. Note that if the bus is left low for more than t
low period as a reset pulse, effectively terminating the transaction.
When performing SHA-1 computations, the DS2703 requires a stronger pullup than 4.7k. A P-FET in parallel with
the standard pullup can be switched on during computation and then disabled to read the result. When measuring
the thermistor R
voltage divider with the thermistor. A voltage A/D connected directly to the 1-Wire bus can then read the voltage
drop of the thermistor.
Figure 5. 1-Wire Bus Interface Circuitry
TRANSACTION SEQUENCE
The protocol for accessing the DS2703 through the 1-Wire port is as follows:
§
§
§
§
All transactions of the 1-Wire bus begin with an initialization sequence consisting of a reset pulse transmitted by the
bus master, followed by a presence pulse simultaneously transmitted by the DS2703 and any other slaves on the
bus. The presence pulse tells the bus master that one or more devices are on the bus and ready to operate. For
more details, see the 1-Wire Signaling section below.
PULLUP
Initialization
Net Address Command
Function Command(s)
Data Transfer (not all commands have data transfer)
< 3.0V, a value of approximately 2kW is recommended. The idle state for the 1-Wire bus is high. If, for any
Rx
Tx
Bus Master
Voltage A/D
V
PULLUP
COMM
THM
COMP
PULLUP
, both the strong pullup and standard pullup should be disabled to allow a weak pullup to form a
≥ 3.0V, a value of approximately 4.7kW is recommended. For long line lengths and/or
4.7K
50K
11 of 20
PACK-
DQ
150
LOW0
R
THM
, slave devices on the bus begin to interpret the
~1µA
DS2703
~100Ω
MOSFET
Activate
THM
Rx
Tx