PDT-11/150 down

Tony Duell 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.


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