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View Full Version : Undocumented "SCRATCH" use for PET?



Keal
April 18th, 2009, 02:20 PM
I may have found an undocumented Commodore command for PET.

"SCRATCH *,8" and "SCRATCH *,9", if I recall correctly from when the command broke my computer, doesn't error out on a PET 4016 Model-N with pet basic 4.0 and a 2031 single sided 5.25" floppy diskette drive, but does seem to glitch a possible PLA (programmable logic array) in the drive.

The two commands seem to have no effect other than lock out directory listing, and it stays locked out permanently until a file is successfully loaded off the same diskette that was in place when it was locked. Apparently, a person can't even load off a different diskette.

Power cycling the drive and computer and even waiting for the capacitors to all bleed off doesn't seem to fix it either.

carlsson
April 19th, 2009, 02:06 AM
Did you ever try to issue the "I" command to initialize the drive? Besides, you misremember the syntax. According to the manual it is like this:

SCRACH "*",Dx ON Uy

x is drive number (0 or 1 on dual drives)
y is device number (8 or 9 if you have an extra disk drive)

If Dx and Uy are omitted, they default to D0 on U8. It is possible your 2031 drive had some error which made the command get stuck?

dave_m
April 19th, 2009, 09:23 AM
I may have found an undocumented Commodore command for PET.

"SCRATCH *,8" and "SCRATCH *,9",

While it has been 25 years since I last used a PET disk drive, I do remember on my 2040 drive that if I switched disks without doing an initialize, it could corrupt the disk. I think later models like the 4040 did an automatic initialization.

Keal
October 21st, 2009, 05:15 AM
Sorry for the long delayed bump!


I figured it out, SCRATCH is one of the first commands that fails along with LOAD when the "IEEE-488 to 24" cable ends up being within a a few months to a year of the absolute end of its lifespan.

There is no PLA, etc, involved; I had a severe brain fart that day.