Commodore PC-10 machine code monitor

[retro]

I recently discovered, quite by accident, that my Commodore PC-10 III has a machine code monitor in ROM BIOS at address F000:0

COMMODORE 8088 Monitor
Pre-release Version 2.0
Copyright 1987 Commodore Technology Group
Use ? for help

CBM88>_

Would anyone know how it's meant to be invoked? I realise I can start it via Debug (g=F000:0) but obviously that's not what was intended.

I can't find any mention of it in the Operator's Manual.
I'm guessing perhaps a special key combination at boot time?

 

[per]

I recently discovered, quite by accident, that my Commodore PC-10 III has a machine code monitor in ROM BIOS at address F000:0

COMMODORE 8088 Monitor
Pre-release Version 2.0
Copyright 1987 Commodore Technology Group
Use ? for help

CBM88>_

Would anyone know how it's meant to be invoked? I realise I can start it via Debug (g=F000:0) but obviously that's not what was intended.

I can't find any mention of it in the Operator's Manual.
I'm guessing perhaps a special key combination at boot time?

Monitors are usually not bigger than a few hundred bytes, and their functionality is about enough to give you the ability to enter and run small machine-code programs. Some systems contains monitors solely for diagnostic purposes, and there may well be a posibility that a special key combination at startup may invoke it.

In order to find out exactly how it may be invoked, you will need to disassemble the system BIOS of the Commodore PC-10, a task which is quite time consuming. It shouldn't nessecarely be too hard since most of the functionality of the PC-compatible BIOS is well known and documented. What you are after is obivously either a call or a jump to F000:0000.

I guess they aren't that uncommon. For example, I have found a 6802-monitor within the firmware of a hardware datalogger I have.

 

[vwestlife]

Zenith PCs had a similar ROM monitor program, which could be invoked by either pressing Ctrl-Alt-Ins or starting up the computer with no bootable disk. So try turning on the Commodore with no hard drive or boot disk, and see if it dumps you into the monitor.

 

[Chuckster_in_Jax]

Zenith PCs had a similar ROM monitor program, which could be invoked by either pressing Ctrl-Alt-Ins or starting up the computer with no bootable disk. So try turning on the Commodore with no hard drive or boot disk, and see if it dumps you into the monitor.

Heath/Zenith's ROM Monitor was one of the best monitors out there. I've never seen any other manufacturer with a monitor with that level of capability. However if Commodore bothered to put something like that in the Colt, it would be interesting to see what it does.

The screen shot shows "Use ? for help" What does it display when '?' is pressed?

 

[retro]

Thanks for the suggestions

Thanks for the suggestions

The screen shot shows "Use ? for help" What does it display when '?' is pressed?

CBM88 Commands

[B]D[/B]ump [starting addr]
[B]F[/B]ill [starting addr] [count] [data]
[B]G[/B]oto [addr] [breakpoint1] [breakpoint2]
[B]I[/B]nput port [byte|word] [port addr]
[B]O[/B]utput port [byte|word] [port addr] [data]
i[B]N[/B]terrupt [#hex]
[B]M[/B]ove [source addr] [dest addr] [count]
[B]S[/B]ubstitute Memory [address]
[B]T[/B]race
e[B]X[/B]amine [register]
[B]B[/B]oot

So try turning on the Commodore with no hard drive or boot disk, and see if it dumps you into the monitor.

Boot disk failure. Type key to retry

In order to find out exactly how it may be invoked, you will need to disassemble the system BIOS of the Commodore PC-10, a task which is quite time consuming. It shouldn't nessecarely be too hard since most of the functionality of the PC-compatible BIOS is well known and documented. What you are after is obivously either a call or a jump to F000:0000.

I was hoping someone might know off the top of their head so I could avoid this but it's probably a good idea anyway. The PC-10 uses a modified Phoenix BIOS. I've disassembled it using Sourcer but it'll take me a while to trawl through it to see what it's up to. Watch this space...