Re: Ribbon Cable

From: Gerrit Heitsch <gerrit_at_laosinh.s.bawue.de>
Date: Tue, 17 Dec 2013 20:35:13 +0100
Message-ID: <52B0A771.2020509@laosinh.s.bawue.de>
On 12/17/2013 08:09 PM, silverdr@wfmh.org.pl wrote:
>
> Those I have donít, but as Gerrit corrected me - it makes sense: there was no intertwining on the original PATA (typical PC crap engineering - like with most PC stuff when compared to the rest..)

Gets even better. There were even IDE-Cards that omitted the 74LS245 
buffers between the ISA slot and the IDE connector. That means that the 
data bus from the ISA slot was directly connected to the HD over a 
40wire cable with no shielding between the signals whatsoever.

The funny thing was, it usually worked.

As for the SX-64... Adding length to an unbuffered, non-terminated data 
and address bus doesn't help with the signal quality. And if you ever 
looked at the signals in a C64, you know they are not very clean to 
begin with.

I sometimes wonder if one could improve stability if one removed the 
pullups for A12 to A15 and replaced them with a 74LS125. The inputs 
connected to +5V, the enable signals to AEC. That way A12 to A15 would 
no longer slowly float up to +5V when VIC takes over the bus but get 
pulled HIGH quickly. Maybe the same for R/_W.

Another detail I'd take a closer look at would be the 7406/pullup combo 
that tristates the output the 74LS257 multiplexers when it's VIC's turn. 
Replace it with a real driver (74LS04).

  Gerrit



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