Datasheet

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
T
S
T
H
D03IN1416
T
CC
T
DS
T
CR
T
CR
T
DH
T
S
T
H
T
B
T
CC
CLR_T
RxD
RxTx
TxD
REG_DATA
D03IN1402