AN1714 datasheet(32/46 Pages) STMICROELECTRONICS

32 / 46 page

Demonstration board for ST7538Q

AN1714

32/46

the MCU has to keep the PC4 pin low. The external signal can be applied at the diode

cathode.

Figure 28.

ST7538Q / microcontroller interface

The third group of signals consists of a series of auxiliary signals coming from the ST7538Q

linked to some standard input of the microcontroller.

The CD/PD and BU signals give information about a carrier (or preamble detection)

condition and about the BU condition (according the EN50065-1).

If the zero-crossing comparator is used, the ZCOUT signal gives a digital signal

synchronized with the mains phase.

The PG, TOUT and REG_OK signals are monitor signals. The PG signal indicates the

correct supply level of the internal 5 V regulator of the ST7538Q (VDC). If the modem

regulator supplies the microcontroller or its reset is connected to the RSTO pin, it is

recommended to monitor this signal. In fact when the PG signal goes down during a

shutdown procedure, the microcontroller can try to correctly stop the running activities (for

example a memory writing) before the UVLO threshold is reached and the entire application

is reset, or before the regulator isn't able to correctly supply the micro. When a PG down is

detected, the transmission is disabled to avoid uncontrolled access to the mains. In any

case a correct shutdown procedure has to be completed to perform a correct reset of the

application.

The TOUT signal is active when a transmission procedure is aborted, either for a time out

event or for an overheat condition.

The REG_OK signal shows corruption of the internal modem register. Pay attention that the

REG_OK function doesn't check uncontrolled control register write procedure, due for

example, to a voltage spike on the REGDATA and RX/TX pins.

ST72C334

ST7538

PC3/ICAP1_B

PC5/MOSI

OSCIN

RESET

PC4/MISO/ISPDATA

PC6/SCKI/ISPCLK

ANI4/PD3

ANI5/PD4

ANI6/PD5

MCO/PF0

PF1/BEEP

PF2

PB1

PB2

PB3

RXD

MCLK

RSTO

TXD

CLRT

REG/DATA

RXTX

ZCOUT

TOUT

REG_OK

ISPCLOCK

J11

R16

D13

ISP RESET

R15

C22

SW1

ISPDATA

ISPSEL

R17

CD/PD

PA3

PB0

PC7/SS