18 Jan
2012
18 Jan
'12
11:24 a.m.
On 17 Jan 2012 at 16:49, Jim Brain wrote:
If you re-read my original post, you'll see I porposed using a
microcontroller (to decode the PS/2 signals) and a crosspoint switch IC.
As Tony notes, KB matrix diodes would make things
more complicated, if
not impossible.
I concocted my soluation after looking at the TRS-80 model 4
schematics.
Clearly, other keyboard schemes will require other solutions. But
I'd still want a MCU to decode the PS/2 keyboard proposed. Maybe
Tony wants to do the decoding with discrete logic, but that would not be my first choice for simplicity, expense or power.
It's not the
PS/2's choice either to the best of my knowledge.
I beleive the PS/2s used a microcontrolelr on the motherboard. The PC/AT
certainly did (an 8042). The PC and PC/XT did not, but then keyboard
protorcol there is a little simpler.
I do feel, though , that in some cases, a microcontroller (or other
programmed devices) adds complexity and makes it more dificult to
understnd or repair the device in the future, I can understnad why
commercial organisations like this, but it does seem rather against the
spirit of classic computing (which to some extent depends on
understnading old machines and being able to repair them).
-tony