Re: Repairing a SFD-1001 (8250/LP, 8050, 4040, 3040, 2040)

From: Jim Brain <>
Date: Wed, 10 Aug 2011 18:05:58 -0500
Message-ID: <>
On 8/10/2011 3:10 PM, Hoffmann-Vetter, Martin wrote:
> Hello,
>> I don't know how relevant it is to CBM floppy drives, but it seems to
>> have something to do with chip select lines?
> That's one problem when you change an 2332 (rom) to a 2532 or 2732 (eprom).
> The 23xx series has many chip select (cs) signals that can be programmed in
> the polarity. So the standard 2332 for the PET is non inverted chip select
> (cs1) at pin 21 and inverted chip select (cs2) at pin 20. You have the same
> problem with some dos roms eg. 901887-01 and 901888-01. That's a 2364 with
> one non inverted chip select at pin 20!
I have been asked to run a modifed 2364 adapter that allows pin 20 to be 
inverted on non-inverted.  I used a hct86 with a jumper to ground on one 
side of the gate to alter the inversion of the line.  It looks like 
there might be value in supporting a 2332 with a similar setup.


The 6540 adapter I have uses a hct138 to support all of the select lines.


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Received on 2011-08-11 00:00:03

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