LZ: 1st report on TI-keyboard link
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LZ: 1st report on TI-keyboard link
Okay... I'm probably going to start work on the wiring today. From what
I've learned so far from Philips Semiconductors, the PC/AT keyboard's 5
pins are one no-connect, 5V power, ground, data, and a clock line. When
a key is pressed, a 11-bit packet of data ( and corresponding clock pulses )
are sent that include an 8-bit scan code, odd parity bit, and start/stop pulses.
A second scan code is sent when the key is released. This is also how multiple
key presses are handled (IE Ctrl+A = Ctrl-down,A-down,A-up,Ctrl-up)
The original working schematic supplied by Philips involved a 11 MHz 8051 series
microcontroller that translated the 11-bit data packet into an 8-bit ASCII code,
while functioning as a I2C bus slave ( master can recieve the most recent byte
using a read signal... ) I was worried about the speed of my I2C routines on
the calc, and also the matter of programming the microcontroller, which has its
own code and RAM.
>From observing the process and schematics, I've decided to attempt forgoing the
controller chip and the $15 of electronics going with it, and try linking to the
keyboard directly. At this point, I'm going to try using a 9V battery dropped
to 5V for power, and use the two data lines for clock and data. I can't
remember
( someone help plz? ) if the ground is reverse polarity, ie 5V instead of
usu. 0V,
though I'm sure the data lines are as such. Without all the electronics, I
think
just the DIN plug will be needed, and maybe a protecting resistor or two.
( Do you guys want a larger DIN-5 plug, which is most, or the smaller PS/2 plug?
I suppose I could build them both into my prototype, the only difference is a
sixth pin which luckily is a no-connect. )
Thanks for listening,
Ryan J. Myers ( Webmaster ) rmyers@inetarena.com (ICQ UIN 1473314)
Portland, Oregon ( US ) http://boris.inetarena.com/
"Nolite tes bastardes carborundum." - Margaret Atwood
"C> REALITY.SYS is corrupt, reboot universe? (Y|N)" - Anonymous
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