ST7540 datasheet(26/44 Pages) STMICROELECTRONICS

26 / 44 page

Functional description

ST7540

26/44

Figure 14. CD_PD Timing during RX

Figure 15. Receiving path block diagram

6.7

Transmission mode

The transmission mode is set when RxTx Pin =”0” and REG_DATA Pin =”0”. In transmitting

mode the FSK Modulator and the Power Line Interface are turned ON. The transmit Data

(TxD) enter synchronously or asynchronously to the FSK modulator.

●

Synchronous Mains access: on CLR/T rising edge, TxD Line Value is read and sent to

the FSK Modulator. ST7540 manages the Transmission timing according to the

BaudRate Selected

●

Asynchronous Mains access: TxD data enter directly to the FSK Modulator.The Host

Controller manages the Transmission timing

In both conditions no Protocol Bits are added by ST7540.

The FSK frequencies are synthesized in the FSK modulator from a 16 MHz crystal oscillator

by direct digital synthesis technique. The frequencies Table in different Configuration is

reported in Table 8. The frequencies precision is same as external crystal one’s.

TDCD

TCD

CD_PD

RX_IN

D03IN1418

TDCD

TCD

RxD (UART/SPI="1")

demodulation active on RxD pin

RxD (UART/SPI="0")

noise demodulated

Low Pass

Band Pass

PRE-FILTER

IF FILTER

FSK

DEMODULATOR

DIGITAL

FILTER

MIXER

CARRIER/

PREAMBLE

DETECTION

AGC

GAIN

CONTROL

LOCAL

OSC

Bit 23

Bits 0 -2

Bits 3-4 &14

Bits 0-2

RX_IN

Bits 9-10

Bits 12-13 & 22

Carrier Detection

RxD

CLR/T

CD_PD

BU/THERM

PLL

Bits 3-4

Low Pass

BAND

USE

Bits 3-4 & 22

Band Pass

CHANNEL

FILTER

Band Pass

D03IN1419

HEADER

RECOGN.

Bits 18-21 &

24-47

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