Re: Calling all DOS-heads

From: Nate Lawson <>
Date: Fri, 30 Mar 2012 09:30:04 -0700
Message-Id: <>
Here are the decodings:

On Mar 29, 2012, at 5:54 PM, Jim Brain wrote:

> I bow to the knowledge of those who understand DOS better than I, but I am confused about the operation of the ATNACK circuit in the 1541.
> Now that I finally have a good PC-based logic analyzer, I submit two traces for perusal:
> load"$",9

ATN - 29 F0 (open 9, 15)
24 30 ('$0')
ATN - 3F (close 15)

> If I then remove pin 10 of UB1 (the '06 that outputs the result of the ACK circuit onto the DATA line), I get this trace

Using this pic:

Same as before, but during the close (3F), Ingo is right that the drive is not in the main loop because it is servicing the dir request and thus it doesn't get back to reading the flag set by the IRQ handler to say that it should release DATA.

The question is, why doesn't it ever get back to that point, maybe a few seconds later?


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Received on 2012-03-30 17:00:10

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