PC87365 datasheet(139/215 Pages) NSC

139 / 215 page

7.0 WATCHDOG Timer (WDT) (Continued)

139

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7.3.4

WATCHDOG Status Register (WDST)

This register holds the WATCHDOG Timer status, which reflects the value of the WDO pin and indicates that the timeout

period has expired.

On reset or on WATCHDOG Timer activation, this register is initialized to 01h.

Location:

Offset 02h

Type:

7.4

COUNTING DOWN IN SECONDS

To select seconds (instead of minutes) as the time unit used by the WATCHDOG Timer to countdown:

1. In the WDST register (see Section 7.3.4), write 80h to set bit 7 to ‘1’.

2. In the WDST register, write 84h to set bit 2 to ‘1’.

3. In the WDTO register (see Section Section 7.3.2), set the number of seconds to countdown (in Hexadecimal notation,

for example, ‘0A’ is 10 seconds, ‘FF’ is 255 seconds).

7.5

WATCHDOG TIMER REGISTER BITMAP

Bit

76543210

Name

Time Unit

Reserved

Time Unit

Reserved

WDO Value

Reset

00000001

Bit

Description

Time Unit.

0: Minutes (default)

1: Seconds (see Section 7.4)

6-3

Reserved.

Time Unit.

0: Minutes (default)

1: Seconds (see Section 7.4)

Reserved.

WDO Value. This bit reﬂects the value of the WDO signal (even if WDO is not configured for output).

0: WDO active

1: WDO inactive (default)

Bits

Offset

Mnemonic

00h

WDTO

Programmed Timeout Period

01h

WDMSK

Reserved

Serial Port 2

IRQ

Trigger

Enable

Serial Port 1

IRQ

Trigger

Enable

Mouse IRQ

Trigger

Enable

KBD IRQ

Trigger

Enable

02h

WDST

Time Unit

Reserved

Time Unit

Reserved

WDO

Value

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