KSI-W002-000

12

6.11 Watchdog timer (WDT)

The watchdog timer provides the means to return to a reset condition when a system

malfunction occurs and the program enters an infinite loop caused by noise or any

abnormal state.

Also this timer have a function of oscillation stabilization timer. This is a 13-bit counter,

counts the clock which is divided twelve (F

stops but when a key input is detected (Port D, Port E) oscillation starts. When 12288 clock

cycles have been counted, the program will be executed from reset address (000H). If the

port C data register’s value does not change from “L” to “H” before the timer counts 98304

clock cycles, a device reset condition is generated.

The oscillator stabilization time : 12/F

The time-out period

: 12/F

Figure 6-4. Function of Watchdog Timer

SD6830

Watchdog Timer (13-bit)

CLK

RESET

OPSTART

Operating Start

Fsys/12

Power-on Reset Active

Stop Mode Active

PORT C Data : Low to High Transition

OVERFLOW

To Reset Logic

OSCOUT

27mS(Min.)

Normal

mode

Stop

mode

Normal

mode

STOP

Instruction

Watchdog Timer

Overflow

PORT C Data

Low to High

WDT

counting value

98304

12288

Time

PC

0

PORT C Data

Low to High