Datasheet for a NEC Chip in DEC Professional 350

Ed C. edcross at
Sun Nov 4 15:36:26 CST 2018

Just had a look to this manual: Power-Up Self-Tests, this section mentions the existence of rom
containing basic power up tests. I assume you are not even getting there
and your system fails to execute from this rom and report any errors on

In such case, A) is your cpu working? B) Is the rom code correct?

On Sun, Nov 4, 2018 at 10:11 PM Rob Jarratt <robert.jarratt at>

> > -----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
> signal,
> > 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.
> Regards
> Rob

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