Datasheet for a NEC Chip in DEC Professional 350

Rob Jarratt robert.jarratt at
Sun Nov 4 15:11:20 CST 2018

> -----Original Message-----
> From: Eduardo Cruz [mailto:edcross at]
> Sent: 04 November 2018 13:47
> To: rob at; Rob Jarratt <robert.jarratt at>; General
> Discussion: On-Topic and Off-Topic Posts <cctalk at>
> Cc: Tony Duell <ard.p850ug1 at>
> Subject: Re: Datasheet for a NEC Chip in DEC Professional 350
> A constant pulsing reset is usually a watchdog at play. Hardware watchdogs
> are usually implemented in systems to reset everything should the system
> not meet one specific criteria: eg cpu touch one memory address before X
> amount of time, or pcb voltage lower than X volts, etc.
> Watchdogs are also usually found as software routines executed by the cpu
> also looking for specific conditions. These rarely issue a reset hardware
> just restar the program.

It looks to me like the reset is every 10us. I don't know how long the
watchdog is likely to be, the technical manual I have doesn't seem to
mention it in the section on the reset logic. I am still trying to find the
source of the signal that seems to be in the "wrong" state.



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