ST7540 datasheet(21/44 Pages) STMICROELECTRONICS

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ST7540

Functional description

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Synchronous mode:

In Synchronous Mode ST7540 is always the master of the communication and provides

the clock reference on CLR/T line. When ST7540 is in receiving mode an internal PLL

recovers the clock reference. Data on RxD line are stable on CLR/T rising Edge.

When ST7540 is in transmitting mode the clock reference is internally generated and

TxD line is sampled on CLR/T rising Edge.

If RxTx line is set to “1” & REG_DATA=”0” (Data Reception), ST7540 enters in an Idle

State and CLR/T line is forced Low. After Tcc time the modem starts providing received

data on RxD line.

If RxTx line is set to “0” & REG_DATA=”0” (Data Transmission), ST7540 enters in an

Idle State and transmission circuitry is switched on. After Tcc time the modem starts

transmitting data present on TxD line (Figure 8) .

Figure 7.

Receiving and transmitting data/recovered clock timing

Figure 8.

Data reception -> data transmission -> data reception

Transmitting Bit Synchronization

CLR/T

RxD

CLR/T

TxD

Receiving Bit Synchronization

TSTH

D03IN1416

TCC

TDS

TCR

TDH

TSTH

TCC

CLR_T

RxD

RxTx

TxD

REG_DATA

D03IN1402

ST7540 Datasheet(PDF) 21 Page - STMicroelectronics