🚀 go-pugleaf

Yesterday Yours Truly (jcmorris@mwunix.mitre.org wrote:

>walls@saifr00.cfsat.honeywell.com (Gerald Walls) writes:

>> dchivers@engr.UVic.CA writes:
>>>merchant@cbnews.cb.att.com (shahrukh.s.merchant) writes:

>>>> [Typing ^P causes screen output to echo to the printer]

>Once it may have been in BIOS but no more.  If I can find it I'll look at
>the BIOS source for the original 1981 PC to check on this.

>Originally the echo-to-printer function was toggled by CTRL-PrtSc, but
>that seems to have disappeared sometime in the distant past.

>A quick look at the source code for the IBM PC/AT BIOS reveals that if you
>hit CTRL-PrtSc it is recognized as a special case, causing the keyboard
>interrupt handler (int 0x09) to place code 0x0072 in the keyboard buffer.
>(Note that this key combination is defined only for an 88-key keyboard;
>the "enhanced" keyboards put PrtSc on a special-purpose key which sends
>the 0xE0 prefix.)  Testing a few systems in the area I found that CTRL-PrtSc
>has no effect any more.

I dug out of may archives a copy of the BIOS source listings for the original
(1981) PC and found that (like the AT BIOS I noted previously) there's no
special code for ^P, and the CTRL-PrtSc key combination is recognized as
a special case, producing a response of 0x0072 to the INT 0x16 caller.

I didn't look up the DOS V1 manual I've got squirreled away somewhere, but
the IBM PC Technical Reference Manual documents CTRL-PrtSc as the toggle
for screen-to-printer echo.

Joe Morris