Datasheet for a NEC Chip in DEC Professional 350

Rob Jarratt robert.jarratt at
Tue Nov 6 01:18:39 CST 2018

If you know where to find the printset for the 350 then please let me know.

In the absence of a printset i have been reverse engineering the schematic to work out the cause of the resets, i am just having trouble tracing one possible path, and i am away all week so can't look again until the weekend.



Sent from my Windows 10 device

From: allison via cctech
Sent: 06 November 2018 02:24
To: cctech at
Subject: Re: Datasheet for a NEC Chip in DEC Professional 350

On 11/04/2018 08:10 AM, Rob Jarratt via cctech wrote:
>> -----Original Message-----
>> From: Tony Duell [mailto:ard.p850ug1 at]
>> Sent: 04 November 2018 12:42
>> To: rob at; Jarratt RMA <robert.jarratt at>; General
>> Discussion: On-Topic and Off-Topic Posts <cctalk at>
>> 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> 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 ( they are all inputs and not outputs. So I need to look again for an output pin that is driving this signal.
> Thanks
> Rob 
Rob, you need to have the drawing for the PRO-350, and read it.  Reset
on the F11 chipset is generally part of
Pwr-OK  and if reset is bouncing likely power is NOT ok. 

FYI the 7201 is MPSC a dual multiprotocol serial chip not unlike the
Z80-SIO.  Likely the system wide reset
is coming from the power OK generation as you seeing hardware reset into
the MPSC.

Hint: the pro350 is basically an 11/23 in a different form factor.


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