UM0239 datasheet(17/44 Pages) STMICROELECTRONICS

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UM0239

Getting started

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4.2.5

Watchdog

The Watchdog parameter (Bit 6) enables the Watchdog function that generates an internal

and external reset when the internal Watchdog timer expires. The Watchdog timer is reset

by applying a negative pulse on pin WD.

Note:

The ST7 MCU Firmware (on

EVALCOMMBOARD) automatically provides the Watchdog

Timer Reset.

4.2.6

Transmission timeout

The Transmission Timeout parameter (Bits [8:7]) defines the maximum time of continuous

transmission before a Timeout event occurs. In this case, the transmission is interrupted and

the device is set in RX mode.

4.2.7

Detection method

The Detection method (Bits [13:12]) defines the way the modem notifies the presence of a

carrier (CD) or preamble (PD) through the ST7540 CD/PD pin. If the Carrier detection

method is selected, the CD/PD line becomes active when a signal with a harmonic

component close to the programmed Carrier Frequency is detected on the RAI pin. If the

Preamble detection method is selected, the CD/PD line becomes active when a signal with

a carrier modulated at the programmed Baud Rate for at least 4 consecutive symbols

("1010" or "0101") is detected on the RAI pin. If the Detection method is conditioned CLR/T

and RxD signals are enable only when CD/PD line is enable, otherwise CLR/T and RxD are

always enabled.

Table 8.

Watchdog

Bit 6

Value (sec)

Disabled

1.5 (default)

Table 9.

Transmission timeout

Bits [8:7]

Value (sec)

Bits [8:7]

Value (sec)

Disabled

1 (default)

Not used

Table 10.

Detection method

Bits [13:12]

Value

Bits [13:12]

Value

Preamble detection without

conditioning

Carrier detection without

conditioning (default)

Preamble detection with

conditioning

Carrier detection with conditioning

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