ST7538

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AUXILIARY ANALOG AND DIGITAL FUNCTIONS

Band In Use

The Band in Use Block has a Carrier Detection like function but with a different Input Sensibility (77dB

µV

Typ.)

and with a different BandPass filter Selectivity (40dB/Dec).

BU line is forced High when a signal in band is detected.

To prevent BU line false transition, BU signal is conditioned to Carrier Detection Internal Signal.

Time Out

Time Out Function is a protection against a too long data transmission. When Time Out function is enabled

after 1 or 3 second of continuos transmission the transceiver is forced in receiving mode. This function

allows ST7538 to automatically manage the CENELEC Medium Access specification. When a time-out

event occur, TOUT is forced high, and is held high for at least 125 ms. To Unlock the Time Out condition

RxTx

should be forced High. During the time out period only register access or reception mode are en-

abled.

abled and ST7538 must be configured in data reception after the reset event before starting a new data

transmission.

Time Out time is programmable using Control Register bits 7 and 8 (table 6).

Figure 17. Time-out Timing and Unlock Sequence

Reset & Watchdog

RSTO Output is a reset generator for the application circuitry. During the ST7538 startup sequence is

Inside ST7538 is also embedded a watchdog function. The watchdog function is used to detect the occur-

rence of a software fault of the Host Controller. The watchdog circuitry generates an internal and external

be achieved applying a negative pulse on WD pin Fig 18.

Figure 18. Reset and Watchdog Timing

RxTx

TOUT

D03IN1409

RSTO

WD

D03IN1410