ST7538
Transmission Mode
The transmit mode is set when RxTx Pin =”0” and REG_DATA Pin =”0”. In transmitting mode the FSK Mod-
ulator and the Power Line Interface are turned ON. The transmit Data (TXD) enter synchronously or asyn-
chronously 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. ST7538 Manage the Transmission timing according to the BaudRate Se-
lected
– 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 ST7538.
The FSK frequencies are synthesized in the FSK modulator from a 16 MHz crystal oscillator by direct dig-
ital synthesis technique. The frequencies Table in different Configuration is reported in Table 3. The fre-
quencies 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 12.
Bit 7 & 8
29
23
VOLTAGE
LOOP
TIMER
Vsense
CL
7
5
TOUT
THERMAL
SENSOR
CURRENT
LOOP
Bit 14
Bit 0-5
Bit 0-2
19
21
24
TxD
PLI
PLI
PLI
ATOP1
ATOP2
ATO
DAC
ALC
Band Pass
FSK
MODULATOR
TRANSMISSION
FILTER
D-TYPE
FLIP
FLOP
8
CLR/T
ZERO CROSSING
CLR/T GENERATOR
15
ZCOUT
16
ZCIN
D03IN1420
17/30
STMICROELECTRONICS [ ST ]
