Re: Interesting issue with 1541 ATN line

From: Jim Brain <>
Date: Mon, 14 Oct 2013 01:55:27 -0500
Message-ID: <>
On 10/14/2013 12:22 AM, Baltissen, GJPAA (Ruud) wrote:
> Hallo Jim,
>> Strangely, if I reset the drive after disconnecting them (and connecting
>> the two inputs of the '86 together, all works as expected.
> That is correct. The data line should be (H) after a reset. The question is: what pulls it (L) after your disk access? Can only be the drive IMHO, acting on CA1 (you didn't mention disconnecting it).
It's not low after disk access.  In both situations, the DATA line is high.

CA1 and PB7 are both disconnected from the PCB in both situations.

Using this schematic for reference:

PB7 and CA1 are disconnected, and I tie ATN IN to ATNA (tying ATN IN 
from the IEC port to pin 4 of the UG2 74LS86, which should render the 
output always low, making the UD1 7406 always high.

I'll see if I can post some logic traces tomorrow night.

I *think* it is because ATN IN floats high if I disconnect it, and the 
code handles that differently immediately after reset than after a 
successful disk access.  I guess I'll need to tie it low when ATN is 

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Received on 2013-10-14 07:00:18

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