DEC 8640 Pinout

[Rob Jarratt]

> -----Original Message-----
> From: Tony Duell [mailto:ard.p850ug1 at gmail.com]
> Sent: 28 October 2018 18:15
> To: rob at jarratt.me.uk
> Cc: General Discussion: On-Topic and Off-Topic Posts
> <cctalk at classiccmp.org>
> Subject: Re: DEC 8640 Pinout
> 
> On Sun, Oct 28, 2018 at 6:10 PM Rob Jarratt <robert.jarratt at ntlworld.com>
> wrote:
> 
> > 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?
> 
> 
> No idea how the pins are numbered. But the Pro380 printset seems to show
> pin 2 as the polarising key.And the pin at the other end of the connector is
> logic ground which you must be able to check.
> 

Knowing the 8640 pinout now I was able to trace one of its inputs to the PSU connector, which appears to confirm that DC OK is next to the polarising pin. I can now confirm that DC OK is stable. It seems from my reverse engineering of the schematic that this allows other signals to control the reset state of the F11, but these other signals appear to be driven by clock signals, which is rather confusing at the moment.

> That printset includes a schematic of the PSU which might help too.
> 
> -tony