Datasheet for a NEC Chip in DEC Professional 350

[Warner Losh]

I know that the Rainbow's AFU watchdog was the bane of my existence back in
the day... It would fire if interrupts were disabled too long.

Warner

On Sun, Nov 4, 2018 at 6:47 AM Eduardo Cruz via cctalk <
cctalk at classiccmp.org> wrote:

> 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.
>
> Sent from my iPhone
>
> > On 4 Nov 2018, at 14:10, Rob Jarratt via cctalk <cctalk at classiccmp.org>
> wrote:
> >
> >
> >> -----Original Message-----
> >> From: Tony Duell [mailto:ard.p850ug1 at gmail.com]
> >> Sent: 04 November 2018 12:42
> >> To: rob at jarratt.me.uk; Jarratt RMA <robert.jarratt at ntlworld.com>;
> General
> >> Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
> >> Subject: Re: Datasheet for a NEC Chip in DEC Professional 350
> >>
> >> On Sun, Nov 4, 2018 at 12:37 PM Rob Jarratt via cctalk
> >> <cctalk at classiccmp.org> wrote:
> >>>
> >>> I have posted previously about a DEC Pro 350 I am trying to get
> >>> working again. At the moment it seems to be constantly resetting the
> CPU.
> >>>
> >>>
> >>>
> >>> I have traced one possible path for the cause of this back to a NEC
> >>> chip for which I cannot find a datasheet. It is a 40-pin DIP it is
> >>> marked "NEC Japan
> >>> 8239K6 D7201C". All I have been able to find is more modern USB host
> >>> controllers.
> >>
> >> Almost certainly a uPD7201 multi-protocol (asynchronous and synchronous)
> >> serial chip. I have an NEC data book with it in if all else fails but a
> google
> >> search for 'uPD7201 datasheet' (no quotes) found sites with the data
> sheet
> >> to download as a .pdf file.
> >>
> >> Quite why that should reset the machine is beyond me....
> >
> > I have been trying to find what is driving this path in the logic and
> this chip was the only one I for which I couldn't identify the pins, but it
> seems that from this datasheet (
> https://datasheet4u.com/datasheet-pdf-file/1098405/NEC/UPD7201/1) they
> are all inputs and not outputs. So I need to look again for an output pin
> that is driving this signal.
> >
> > Thanks
> >
> > Rob
> >
>