Re: U0>M1 on the 1571

From: Ruud Baltissen (
Date: 2001-10-17 10:06:27

Hallo Nick,

> it definitely involves some mechanical noises.

Just before ending the routine it checks if the disk has to be initialised.
Could be a try to read the BAM.

> Do you know what comes after the check for 1 or 0.

It first steps to 2 MHz by setting PA5 and then does some LDA's and STA's on
some places for redirecting some IRQ-vectors, changing some flags and
chinging the timer in the $1C00-6522. Not those things that could cause the
effect you described.

> It needs to step-up to
> 2MHz, could the circuit associated with this be the cause?

No. Check the SCH yourself at FUNET. PA5 just steers a 175 that divides the
clock by two or not.

Remark: the above is all _AFAIK_. So I could have missed things that could
cause the behaviour you observed.
  / __|__
 / /  |_/     Groetjes, Ruud
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