18 Jan
2012
18 Jan
'12
11:20 a.m.
On 18 Jan 2012 at 13:57, Curt @ Atari Museum wrote:
There are a lot of adapters (Atmel and PIC) that will
take a PS/2
keybaord and make it into a USB device.... those would be a very good
start as you'd have 1/2 of the work down, next you'd want to guy the
VUSB core out of the code, then take the input from the PS/2 and set
of the ports of the microcontroller for output, setup a row and column
and create your matrix and then build the hardware with some diodes
for the outputs to avoid debounce and and other issues.
I'm not following--the code to interface to a PS/2 keyboard is no big
deal--see the PS/2-to-XT converter I did for the VC forum using an 8-
pin PIC MCU. In this situation, a 20-pin ATTiny2313 would be more
than adquate.
The Model 4 uses 8 bits from the address lines and 8 bits of the data
lines in a system-defined space. Essentially, the keyboard interface
represents 256 bytes of memory where the contents change depending
upon what key is pressed.
Since the PS/2 keyboard does its own debouncing, I'm having a problem
figuring out what the diodes are for.
Jim and Tony proposed using an 8x8 crosspoint switch IC; I proposed
using a dual-ported 256 byte RAM. as an alternative. I'll admit that
I haven't checked prices on either; it could be that the crosspoint
switch IC is cheaper than the DP RAM.
In either case, I don't see the need for debouncing (although the TRS-
80 probably has code to do it). Maybe you were thinking about using
an array of 256 relays?
Just color me dense today.
--Chuck