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HA16117F

CMOS Watchdog Timer

Renesas Electronics 

HA16117F Series

Timing Waveforms and Functional Description

VTL

VCC

P-RUN

Crash

t RH

Watchdog function on

RES

t ON

t OFF

t ON

(VACC = "Low")

t RL

Watchdog function off

RES

t ON

t ON

(VACC = "High")

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 ISTBY

of only 43 µA Typ when the watchdog function is switched 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 (tSL) has elapsed,

RES is output if the P-RUN signal from the MPU is still abnormal.

ACC pin

RES (due to MPU crash)

Adjust according to

MPU's setup time

t SH

t SL

Figure 2 ACC Pin and RES Output

Rev.3.00 Jun 15, 2005 page 6 of 30

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