Re: Commodore 65 and DIN8 cable

From: Michał Pleban <>
Date: Fri, 04 Mar 2016 11:15:23 +0100
Message-ID: <>
Hello! wrote:

> There are two problems with the above - first I was looking at the wrong page of the schematics - so the above should read U3 rather than U1, be then this doesn't seem to be valid either as U3 on your board is a small PAL chip rather than the FDC in question. That's why I put a "valid" qualifier before the "schematics" in my first post referring to the schematics. I /guess/ it's the U22 on your board.

It's called U3 on the schematic, but it's the schematic for rev. 2A. On
our rev. 2B boards this is U22.

Please also note that U22 does not drive the RDATA signal. The currently
selected disk drive is driving this signal. The problem arises because
this line is shared among all drives so it is directly exposed on the

Actually, now that I look at the schematic, I see that this line is
pulled up with 470 Ohm resistor. Quite possibly, the output from the
drive is open collector and needs such pullup, which is too weak
compared to the capacitance of the cable.

All the other lines on the connector are driven directly by U22 and they
do not exhibit this problem.


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Received on 2016-03-04 11:00:11

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