15 Jun
2011
15 Jun
'11
11:08 a.m.
Ok, progress on checking out this Sorcerer BASIC ROM-PAC..
I diescovered there was no way you could exit to the monitor program if you
had a hung ROM-PAC plugged in BUT....I figured out a way to check the
content of the ROM-PAC ROMS.
In the Sorcerer the ROM-PAC occupies space from C000-DFFF using 4 chips.
Reading the docs I saw that the boot up sequence jumps to DFFD or DFFA
depending on if it's a warm or cold start. However, if it finds nothing
there, it assumes there is no ROM PAC attached and boots up the monitor.
YES! This means all I needed to do is remove the number 4 IC (D800-DFFF)
and I should be able to boot to the monitor and then examine the contents of
the three lower ICs. I could then substitute the number 4 IC for one of the
lower ones and examine its contents too.
Soundn very sensible.
I removed the number 4 chip, plugged in the ROM-PAC and booted. Success, I
was in the monitor. I then dumped the memory locations corresponding to the
ROMS. The two lower ICs (C000-CFFF) showed all different hex numbers. In
other words it looked like it contained good code. However, the third IC
I often find doing an ASCII dump as well as a hex one helps. You can
often spot keyword tables, error messages, etc. And if you see them
repeated, it's likely there's some addressing problem so that the same
lcoation appaar at 2 processor addresses.
(D000-D777) contained all zeros!! I then swapped
over the D800-DFFF chip
I'd removed into the socket which originally contained the D000-D777 and
checked that number 4 chip. The code looked good and I could even see the
bootstrap code at the end at DFFD and DFFA (of course it was at location
D7FD and D7FA as I had this number 4 chip in socket 3).
Right. Soundsl ike the address decoding logic is working fine, then.
Conclusion. It's the number 3 IC which is faulty.
I would agreewith you there.
-tony