DEC 8640 Pinout

[Rob Jarratt]

> -----Original Message-----
> From: Tony Duell [mailto:ard.p850ug1 at gmail.com]
> Sent: 28 October 2018 18:04
> 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: DEC 8640 Pinout
> 
> On Sun, Oct 28, 2018 at 5:53 PM Rob Jarratt via cctalk <cctalk at classiccmp.org>
> wrote:
> >
> > I am trying to trace the reason why the CPU on my Pro 350 is
> > apparently being constantly reset. I have reached a DEC 8640 chip.
> > Does anyone have a pinout for it, perhaps even a datasheet, so I can
> > understand what it is supposed to do and whether the pin is an input or an
> output?
> >
> 
> I've sent the data sheet by private e-mail.
> 
> Have you looked at the Pro380 printset on bitsavers? The reset input on the
> J11 chip  in that machine comes from the DCOK pin on the power supply (Pin
> 1 of the PSU connector). It's also buffered by an 8640 for other bits of the
> systen. I would not be surprised if the Pro 350 is similar.
> 
> Are you_sure_ the DCOK pin on the power supply is stable and not
> oscillating?
> 


Thanks for the datasheet. I have to say I am not totally convinced that I have correctly identified the reset pin on the F11 because there seems to be a lot of logic behind it. This particular path I am pursuing now seems a bit more promising though. I have not checked the DC OK pin yet as I wasn't sure which one it was and I was hoping my tracing would take me back to the PSU, but I haven't reached it yet. I suppose I have been assuming that the LED means it is OK, but perhaps it isn't. Hopefully this 8640 will take me closer. When you say it is pin 1 on the connector, which side are you counting from?

Thanks

Rob