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HA16129

Single Watchdog Timer

Hitachi -> Renesas Electronics 

HA16129FPJ

tON

tON is the time from the point the NMI output goes high when power is first applied to the point the RES

output goes low. tON is the time for the potential of the CR pin to reach VthHcr1 from 0V.

tr

The time tr is the fixed delay time between the point the NMI output goes from low to high after the power-

supply voltage comes up to the point RES goes from low to high. The time tr is the time for the CRES pin

potential to fall from the high voltage (about 1.9V) to Vthcres.

tRES

The time tRES is the fixed delay time between the point the NMI output goes from high to low when the

power-supply voltage falls to the point RES goes from high to low. The time tRES is the time for the CRES pin

potential to rise from 0V to Vthcres.

WDT Function

This function determines whether the microprocessor is operating normally or has entered a runaway state

by monitoring the duty or frequency of the P-RUN signal. When this function recognizes a runaway state,

it outputs a reset pulse from the RES pin and sets the OUTE pin to low from high. It holds the RES and

OUTE pins fixed at high as long as it recognizes normal microprocessor operation.

In this function, the potential of the Cf capacitor is controlled by the P-RUN signal. This Cf pin potential

charges the capacitor CR that controls the reset pulse to be between VthLcf and VthHcf. The judgment as

to whether or not the microprocessor is operating normally, is determined by the balance between the

charge and discharge voltage on the capacitor CR at this time.

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