DS2703 SHA-1 Battery Pack Authentication IC

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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

W is recommended. For long line lengths and/or

W is recommended. The idle state for the 1-Wire bus is high. If, for any

reason, a bus transaction must be suspended, the bus must be left in the idle state to properly resume the

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

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:

§

Initialization

§

Net Address Command

§

Function Command(s)

§

Data Transfer (not all commands have data transfer)

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.

Bus Master

DS2703

Rx

Tx

4.7K

50K

150

~100Ω

MOSFET

~1µA

Rx

Tx

Activate

THM

PACK-

DQ

COMP

COMM

Voltage A/D