1541 -> 2031

From: Marko Mäkelä (msmakela_at_cc.hut.fi)
Date: 2000-09-11 07:56:09

I almost forgot to give a progress report on my 1541-IEEE488 modification.
The second EPROM arrived last week, and it appeared to work.  The motor
stops very early in the RESET sequence; if I remove the $c000 ROM, it
starts spinning again when the blinking pattern appears.

However, I have a problem.  The drive and my 8032-SK won't communicate.
Sometimes the PET hangs up; most of the time it says "device not present".
When I got the computer, the user port and the IEEE-488 port were
connected with each other.  I looked at the schematic diagram back then
and came up with the conclusion that nothing should have been broken by
that.  Anyway, now it's a bit frustrating to do any trouble-shooting,
since I don't know whether it is the drive or the computer that is acting
up.  Pasi, you have a working PET, don't you?

One thing that could give some trouble-shooting hints is the voltage I
measured from the IEEE-488 connector.  When I powered up the disk drive
but left the PET turned off, there were some 1.4 volts between ATN and
GND.  After turning on the PET, the voltage rose to some 3.3 volts.
Issuing a floppy command lowered the voltage (as displayed by a digital
multimeter) by a few millivolts for one sample.  This indicates that
something is happening on the bus.  I should take the computer and the
drive to an oscilloscope some day.


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