Printer Port

[Arie de Muynck]

"Jan Panteltje" <pNaonStpealmtje@yahoo.com> wrote in message
news:c8av91$rj5$1@news.epidc.co.kr...

Nope, not guessin, in the 80ties I had the IBM BIOS listing.
And full diagrams of cause (company workled with IBM).
The Keyboard was one half of the 8255 PPI, 8 bit parallel in,
and that was fed from some shift registers, serial clock to the keyboard,
data from / to the keyboard.
Some other bits were control I think. But was not the other half of
that 8255 used for the printer port?
Or was the printer port just a latch?

I looked them up (still have copies of the tech ref manuals with listings
and all diagrams):
- 8255 was indeed used for keyboard control, shiftreg was LS322, and for
some other I/O control
- LPT was not on the mainboard at all! Build on video card or a separate
card with 2x LS374 1x LS244 1x LS240 1x7405, some glue logic, decoding, a
LS245 as data bus buffer.

The manuals were a good investment: they showed how I could add a MUX chip
in an empty position and quadruple the DRAM size on the board from 256KB max
to 1MB max. Much cheaper than the memory expansion boards, and the
conversions I did payed well.

Regards,
Arie de Muynck

 

[Jan Panteltje]

On a sunny day (Tue, 18 May 2004 23:15:47 +0200) it happened "Arie de Muynck"
<Sorry_I_hate_spam@nomail.com> wrote in
<40aa7d1e$0$560$e4fe514c@news.xs4all.nl>:

"Jan Panteltje" <pNaonStpealmtje@yahoo.com> wrote in message
news:c8av91$rj5$1@news.epidc.co.kr...
Nope, not guessin, in the 80ties I had the IBM BIOS listing.
And full diagrams of cause (company workled with IBM).
The Keyboard was one half of the 8255 PPI, 8 bit parallel in,
and that was fed from some shift registers, serial clock to the keyboard,
data from / to the keyboard.
Some other bits were control I think. But was not the other half of
that 8255 used for the printer port?
Or was the printer port just a latch?

I looked them up (still have copies of the tech ref manuals with listings
and all diagrams):
- 8255 was indeed used for keyboard control, shiftreg was LS322, and for
some other I/O control
- LPT was not on the mainboard at all! Build on video card or a separate
card with 2x LS374 1x LS244 1x LS240 1x7405, some glue logic, decoding, a
LS245 as data bus buffer.

The manuals were a good investment: they showed how I could add a MUX chip
in an empty position and quadruple the DRAM size on the board from 256KB max
to 1MB max. Much cheaper than the memory expansion boards, and the
conversions I did payed well.

Regards,
Arie de Muynck
Great I never ventured to modify the main board, I did modify some Hercules

graphics cards later on.
So we could have 4 in a PC.
JP