ard at p850ug1.demon.co.uk
Wed Oct 18 19:07:51 CDT 2006
> > Of course, even the original 5150 had a serial port--most people just tend
> > not to think of it as such. Namely, the keyboard interface. When the AT
> > came along, it was fully bidirectional.
> Interesting thought. I have some XT-class hardware around still, but it's
And a 5150 or 5160 (not sure about the later machines) can _boot_ from
the keyboard connector. If it gets a particular byte back at power-on, it
assumes there's a diagnostic tester connected. The next 2 words are the
number of bytes (? maybe words) to load, then it reads in the data and
stores it in memory starting at a known address. It then jumps to the
first byte loaded.
All this is documented in the BIOS source listings and AFAIK nowhere else.
More information about the cctalk