Datasheet for a NEC Chip in DEC Professional 350

[Rob Jarratt]

> -----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