Datasheet

Functional description ST7538Q
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5.8 Transmission mode
The transmit 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.
● Host Controller Synchronous Communication Mode: on CLR/T rising edge, TXD Line
Value is read and sent to the FSK Modulator. ST7538Q Manages the Transmission
timing according to the BaudRate Selected
● Host Controller Asynchronous Communication Mode: TXD data enter directly to the
FSK Modulator.The Host Controller Manages the Transmission timing
In both conditions no Protocol Bits are added by ST7538Q.
The FSK frequencies are synthesized in the FSK modulator from a 16MHz crystal oscillator
by direct digital synthesis technique. The frequencies Table in different Configuration is
reported in Ta ble 7. The frequencies precision is same as external crystal one’s.
In the analog domain, the signal is filtered in order to reduce the output signal spectrum and
to reduce the harmonic distortion. The transition between a symbol and the following is done
at the end of the on-going half FSK sinewave cycle.
Figure 13. Transmitting path block diagram
TRANSMISSION
FILTER
FSK
MODULATOR
D-TYPE
FLIP
FLOP
DAC
21
19
8
5
24
7
TIMER
THERMAL
SENSOR
VOLTAGE
LOOP
CURRENT
LOOP
CLR/T GENERATOR
ZERO CROSSING
23
29
Vsense
CL
ATOP2
ATOP1
ATOCLR/T
TxD
TOUT
16
15
ZCIN
ZCOUT
Bit 14
Bit 0-5
Bit 0-2
Bit 7 & 8
Band Pass
PLI
ALC
PLI
D03IN1420
Bits 17 & 21