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!