HA16129FPJ Datasheet, PDF (6/23 Pages) Hitachi Semiconductor – Single Watchdog Timer

HA16129FPJ
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 C_R 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
• t_RH
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 C_R potential to reach VthLcr from VthHcr1.
• t_RL
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 C_R potential to reach VthHcr1 from VthLcr.
• t_OFF
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 C_R pin will be about Vout − 0.2 V
(although this value may change with the P-RUN signal input conditions, so it should be verified in the actual
application circuit) and t_OFF is the time for the C_R pin potential to reach VthLcr from that potential.
• t_ON
t_ON is the time from the point the NMI output goes high when power is first applied to the point the RES output goes
low. t_ON is the time for the potential of the C_R pin to reach VthHcr1 from 0 V.
• 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 1.9 V) to Vthcres.
• t_RES
The time t_RES 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 t_RES is the time for the C_RES pin potential to
rise from 0 V 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 C_R 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 C_R at this time.
Rev.3.00 Jun 15, 2005 page 6 of 22