Re: Odd behavior of Disk II in a GS

[dempson@swell.actrix.gen.nz (David Empson)]

In article <CHu2wu.C86@news2.cis.umn.edu> sava0017@gold.tc.umn.edu (Tim Savage) writes:
> 
> Anyways, I plugged the controller into slot 6, and typed PR#6 from a basic
> prompt. The computer locked up. So, I shutdown and moved the card to slot
> 7. Again, from a basic prompt, I type PR#7, and it works. Now I'm bummed
> out because I figure something is wrong with my GS. But here's the
> completely weird part. The next time I go to boot the drive, I type PR#6,
> out of habit, and say 'oops' as a hit return, but to my amazement, the
> drive boots anyhow!

There is a good reason for this.  If you have set slot 6 to "Your
card" and there is no card in the slot, then the processor will be
executing random code from $C600 to $C6FF.  It often seems to be the
case that it ends up at $C700 anyway (i.e. doesn't hit any branch,
jump, call, return or break instructions) and falls into the code which
boots slot 7.

If nothing happens when you try to boot from the card with it in slot
6, you probably have a damaged SlotMaker chip on your motherboard.  The
only way to fix it is to replace the motherboard.

You may be able to narrow down the problem somewhat.  With the card in
slot 6 (and slot 6 set to "Your Card"), try rebooting.  While it is in
the "hang" state, press Control-Reset, which should drop you into BASIC.

Now type the following commands (don't type in the prompt character):

]CALL -151
*C600L

You should see a series of machine code instructions, starting with:

00/C600- A2 20     LDX #$20
00/C602- A0 00     LDY #$00
00/C604- xx 03     xxx $03
00/C605- xx 3C     xxx $3C

I can't rememeber which instructions they are - it is the operands
which are important.

If this looks more or less correct, then the problem is likely to be
with the device I/O locations.  Try turning on the disk drive manually:

*C0E9

Ignore the value the monitor prints in response to this.  The disk
drive should start to spin immediately.

Whether or not this happens, type the following command next:

*C0E8

This tells the disk drive to stop spinning (it takes a second to stop
completely).

Let me know which of the above commands appeared to work properly, and
I can probably tell you what the fault is.  E-mail me to discuss this
further.


It could also be a problem with your TransWarp, but the SlotMaker is
a more likely culprit.
-- 
David Empson                                                               
dempson@swell.actrix.gen.nz                                                
Snail mail: P.O. Box 27-103, Wellington, New Zealand