DS2751E-025 Просмотр технического описания (PDF) - Maxim Integrated

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DS2751E-025

Multichemistry Battery Fuel Gauge

Maxim Integrated 

Figure 12. 1-WIRE CRC GENERATION BLOCK DIAGRAM

MSb

XOR

XOR

DS2751

INPUT

LSb

XOR

HARDWARE CONFIGURATION

Because the 1-Wire bus has only a single line, 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 connect to the

bus with open-drain or tri-state output drivers. The DS2751 uses an open-drain output driver as part of the

bidirectional interface circuitry shown in Figure 13. If a bidirectional pin is not available on the bus

master, separate output, and input pins can be connected together.

The 1-Wire bus must have a pullup resistor at the bus-master end of the bus. For short line lengths, the

value of this resistor should be approximately 5kW. 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 in order to properly

resume the transaction later. If the bus is left low for more than 120ms, slave devices on the bus begin to

interpret the low period as a reset pulse, effectively terminating the transaction.

Figure 13. 1-WIRE BUS INTERFACE CIRCUITRY

BUS MASTER

VPULLUP

(2.0V to 5.5V)

DS2751 1-WIRE PORT

4.7kW

Rx

Rx

1mA

Tx

Typ.

Tx

Rx = RECEIVE

Tx = TRANSMIT

100W

MOSFET

TRANSACTION SEQUENCE

The protocol for accessing the DS2751 through the 1-Wire port is as follows:

§ Initialization

§ Net Address Command

§ Function Command

§ Transaction/Data

The sections that follow describe each of these steps in detail.

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