ST7540 datasheet(36/44 Pages) STMICROELECTRONICS

36 / 44 page

Auxiliary analog and digital functions

ST7540

36/44

Auxiliary analog and digital functions

7.1

Band in use

The Band in Use Block has a Carrier Detection like function but with a different Input

Sensitivity (83.5 dB

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

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

To prevent BU/THERM line false transition, Band in Use signal is conditioned to Carrier

Detection Internal Signal. This function is enabled only in Receiving mode (in Transmission

mode the BU/THERM pin is used for Thermal shutdown signaling, see Section 7.8: Thermal

shutdown).

7.2

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 ST7540 to automatically manage the CENELEC

Medium Access specification. When a time-out event occur, the transmission section is

disabled 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 enabled.

During Reset sequence if RxTx line =”0” & REG_DATA line =”0”, Time Out protection is

suddenly enabled and ST7540 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 12).

Figure 22. Time-out timing and unlock sequence

TOUT

TOFF TOFFD

RxTx

Time Out function

D03IN1409

ST7540 数据表(PDF) 36 Page - STMicroelectronics