HA16117F Series

6

Timing Waveforms and Functional Description

P-RUN

Crash

Watchdog function on

RES

Watchdog function off

RES

Figure 1 Timing Waveforms

Watchdog On/Off Function

A feature of the HA16117F is that watchdog supervision can be switched on and off. When the watchdog

function is switched on, both the supply voltage and

P-RUN input are monitored to detect abnormal conditions. When the watchdog function is switched off

(standby mode), only the supply voltage is monitored. Watchdog supervision is switched on and off by the

input at the ACC pin (pin 7): Supervision is on when ACC is low, and off when ACC is high.

Many MPUs have a standby mode in which the CPU stops running but memory contents are retained. In

standby mode, program execution halts and I/O ports go to the high-impedance state, so there is no need for

the watchdog timer to supervise pulse output from an I/O port to detect abnormal conditions. Power can be

saved by placing both the MPU and HA16117F in standby mode at the same time. The HA16117F is

designed to draw a typical standby current I

off.

ACC Pin (pin 7) and

RES Output

When the MPU returns from standby mode to normal operation it generally takes 10 to 200 ms for the

clock oscillator in the MPU to stabilize. The

RES signal is not output during this setup time. After the

setup time (t

Adjust according to

MPU’s setup time

RES (due to MPU crash)

ACC pin

Figure 2 ACC Pin and

RES Output