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Wanted: Zenith PC/XT ROM BIOS files with DEBUGGER Z-150, etc

mmruzek

Experienced Member
Joined
Sep 28, 2011
Messages
205
Location
Michigan, USA
Hello, One of the unique features of the early Zenith 8088 PC compatibles was a built-in ROM debugger that could be invoked with a special key combination of Ctrl-Alt-Ins. Would anyone happen to have a image/copy of the BIOS ROM they could send me by email? I was only able to find one example doing a web search, and that file had 'may be bad' in the name. (Not the best way to start a project!) Candidate computers might be something named Z-150, Z-151, etc. Thank You, Michael
 

mmruzek

Experienced Member
Joined
Sep 28, 2011
Messages
205
Location
Michigan, USA
I was able to obtain the Zenith 150 BIOS ROM Files by pulling them off some actual chips (using my programmer reader). The files were on 2 chips, 27128 type, with 16K of code each. Thought I would put them here in case someone else has the same interest in exploring the features of the code. Please post your results if you find out anything useful about this code. Also would be interested if anyone has a manual or description of how the Zenith 150 BIOS works, or is organized. Thank You, Michael
 

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  • Zenith 150 ROM.zip
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Trixter

Veteran Member
Joined
Aug 31, 2006
Messages
7,205
Location
Chicagoland, Illinois, USA
Wow, just looking at the dump it looks like you could pull up what was essentially DEBUG.COM right in the middle of program execution! I could have really used that when I was crack^H^H^H^H^Hexploring disassembly in the 1980s. Wait for all the anti-debugger tricks to pass by, then hit the magic key combo.
 

Trixter

Veteran Member
Joined
Aug 31, 2006
Messages
7,205
Location
Chicagoland, Illinois, USA
I was finally able to obtain an 8088-based Zenith system (a ZFA-161-52, one of the luggables designed after the desktop Z-150 series) and sure enough it works as advertised. It's essentially a system monitor set up like DEBUG, with most of the same commands present (Unassemble, Trace, examine Registers, etc). You can also print out a quick color chart for testing the CRT, and entering TEST will go into a test menu where you can test reading the floppy disk, keyboard and memory. It also lets you run the POST multiple times.

What I've been able to figure out:

  • ctrl-alt-ins: Reboot the system into the Monitor
  • ctrl-alt-enter: Immediately enter the Montitor from whatever is currently running (and can execute Go from the monitor to immediately return to it)
  • ESC: at the boot sequence, will immediately go into the Monitor (ie. boot-to-monitor instead of boot from disk).
The embedded Debug has a few extra features that DEBUG.COM doesn't have, such as (B)ooting from a specific device, (V)ideo mode changing (it can still print characters in graphics mode), and also testing the Z-319 Bitmapped Graphics Card (when I try it says not present, so I don't know what the Z-319 is).

This is so awesome. I wish I'd had this in my youth!
 
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