9 Jul
2014
9 Jul
'14
2:39 p.m.
> a model M keyboard with working shift and
enter keys
On Tue, 8 Jul 2014, Philip Belben wrote:
Are you sure? The keyboard I know as the
"Model M" was the AT enhanced
keyboard (and with a different plug and slightly different trim, the
PS/2 keyboard). It is a total anachronism for the 5150. I'm not sure
it would even work with it!
You are absolutely right. Good catch.
The model M was available with several different connectors. Most of the original AT (5170) had a 5 pin DIN connector that
looked the same as the
5150/5160 keyboard connector, but they are elctrically very different.
Actually, I seme to recall tht the signals are the same -- clock, data,
+5V, ground. And on the same pins on both the XT and AT. The 5th pin,
origianlly a reset outptu from the PC to reset the keybaord at power-on
was, AFAIK, never used.
Hwoever, the serial protocol is very different betwee nthe XT and AT
keybaords. So while the clock and data are on the same pins, they
keyboards are not compatible.
I don't remember the name/model number of the 84?
key 5150/5160 keyboard.
It had a model M like feel (buckling springs), but different circuitry.
The origianl PC keyboard is capacitive. The buckling spring flips a flap
onto the PCB, increasign the capacitance betwene traces.
The Type M is, beleive it or not, a membrane contact unit. The flap
pushes the membrane layers together.
I think the 84K PC/AT keybaord is capacitive, but it's been a long tiem
since I've been inside one.
-tony