HA16117F Datasheet, PDF (6/31 Pages) Hitachi Semiconductor – CMOS Watchdog Timer

HA16117F Series
Timing Waveforms and Functional Description
V_TL
V_CC
P-RUN
Crash
t _RH
Watchdog function on
RES
t _ON
t _OFF
t _ON
(V_ACC = "Low")
t _RL
Watchdog function off
RES
t _ON
t _ON
(V_ACC = "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 I_STBY 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 (t_SL) 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
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