Curtis MultiMode 1207B Manual page 44

APPENDIX A: GLOSSARY
A-12
If the voltage continues to drop below the undervoltage level to a severe
undervoltage condition (due to battery drain or external load), the controller
continues to behave in a predictable fashion, with its output disabled.
Watchdog (external, internal)
The external watchdog timer guards against a complete failure of the micropro-
cessor, which would incapacitate the internal watchdog timer. This independent
system check on the microprocessor meets the EEC's requirement for backup
fault detection.
The external watchdog timer safety circuit shuts down the controller (and
the microprocessor) if the software fails to generate a periodic external pulse
train. This pulse train can only be created if the microprocessor is operating. If
not periodically reset, the watchdog timer times out after 150 msec and turns
off the controller. The external watchdog also directly disengages all contactors
and directly shuts down the PWM drive to the MOSFETs. It can only be reset
by cycling KSI.
The internal watchdog timer must be reset periodically by correct sequen-
tial execution of the software. If not reset, the internal timer times out and the
microprocessor is "warm booted." This causes the microprocessor to shut down
its outputs (thus shutting down the controller) and attempt to restart.
Curtis 1207B Manual