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HA16129

Single Watchdog Timer

Hitachi -> Renesas Electronics 

HA16129FPJ

Function Start Voltage

This is the minimum required Vout voltage for the RES, NMI, STBY, and OUTE output pin functions to

start operating. It is stipulated as the voltage that Vout must reach after power is first applied for these pins

to output a low level.

Hysteresis

This is the difference between the LVI function detection voltage when the power-supply voltage drops,

and the clear (reset) voltage when the power-supply voltage rises.

(VHYSN = VNMI' – VNMI; VHYSS = VSTBY' – VSTBY)

OUTE Function

When a microprocessor is in the runaway state, its outputs are undefined, and thus it is possible that the

outputs may be driven by incorrect signals. This function is used to mask such incorrect microprocessor

outputs. When the WDT function recognizes normal operation (when the RES output is high), the OUTE

output will be held high. When the WDT function recognizes an abnormal state and an auto-reset pulse is

output from the RES pin, the OUTE output will be held low. Thus microprocessor outputs during

microprocessor runaway can be masked by taking the AND of those outputs and this signal using external

AND gates.

The OUTE output will go high when the CR pin voltage exceeds VthHcr2, and will go low when that

voltage falls below VthLcr.

There are limitation that apply when the OUTE function is used. Refer to the calculation formulas item for

details.

RES Function

tRH

This period is the length of the high-level output period of the RES pulse when the P-RUN signal from the

microprocessor stops. This is the time required for the CR potential to reach VthLcr from VthHcr1.

tRL

This period is the length of the low-level output period of the RES pulse when the P-RUN signal from the

microprocessor stops. This is the time required for the CR potential to reach VthHcr1 from VthLcr.

tOFF

This is the time from the point the P-RUN signal from the microprocessor stops to the point a low level is

output from the RES pin. During normal microprocessor operation, the potential on the CR pin will be

about Vout – 0.2V (although this value may change with the P-RUN signal input conditions, so it should be

verified in the actual application circuit) and tOFF is the time for the CR pin potential to reach VthLcr from

that potential.

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