4 Nov
2018
4 Nov
'18
5:47 a.m.
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 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
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....