Datasheet

Functional description ST7540
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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 Ta b l e 8 . The frequencies precision is same as external crystal one’s.
T
DCD
T
CD
CD_PD
RX_IN
D03IN141
8
T
DCD
T
CD
RxD (UART/SPI="1")
demodulation active on RxD pin
RxD (UART/SPI="0")
noise demodulated
noise demodulated
Low Pass Band Pass
PRE-FILTER
IF FILTER
FSK
DEMODULATOR
DIGITAL
FILTER
MIXER
CARRIER/
PREAMBLE
DETECTION
AGC
GAIN
CONTROL
LOCAL
OSC
25
Bit 23
Bits 0 -2
Bits 3-4 &14
Bits 0-2
RX_IN
Bits 9-10
Bits 12-13 & 22
Carrier Detection
4
RxD
8
CLR/T
1
CD_PD
7
BU/THERM
PLL
Bits 3-4
Low Pass
BAND
IN
USE
Bits 3-4 & 22
Band Pass
CHANNEL
FILTER
Band Pass
D03IN1419
HEADER
RECOGN.
Bit s 18-21 &
24-47