PS2 encoder to parallel (8bits + strobe signals)

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Hi at all,

is anybody who knows the way to convert a standard ps2 keyboard signals in a
parallel interface TTL 8bits + strobe signals. I not need anything other. I
have a old PC to test on which the keyborad input has a parallel interface
(Z80 PIO).

Thanks to anyone who would give me an help.


Re: PS2 encoder to parallel (8bits + strobe signals)

On Tue, 8 Jan 2008 23:30:47 +0100, "Enrico Lazzerini"

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That won't be easy at all.
If you want TTL 8bits + stobe, I guess you expect ASCII data.
That's not available anywhere in a PC's keyboard communication

A PC keyboard communicates over a 2 wire interface (clock and
data) to an on-board 8042 type controller.
They need eachother to work properly (as you can see when you
use a 'dumb' keyboard switch :-).
The keyboard does not provide character information, just key
down and key release messages. (Key as in 'key location'. that

Then it is up to the OS software to translate a key press into an
ASCII code for the character that is presumably printed on the

If it is just the 8-bit TTL signal you need, I suggest you take
an old(ish) PC with a PS2 keyboard and write a small program that
relays all keypresses to a parallel printer port.

Kind regards,
Gerard Bok

Re: PS2 encoder to parallel (8bits + strobe signals)

I thank for your answers.
I'll try to explain better my problem.
I have to make alive a old Z80 machine that has for input a keyboard
parallel port.
I'd not wish to by a parallel keyboard or a expensive circuit to convert ps2
to parallel way because i not know it the board i want to make alive it will
live again.

So maybe a solution could be to try to redirect the keyboard input also to
the prn or LPT1 port.

Is exists the way?


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Re: PS2 encoder to parallel (8bits + strobe signals)

On Wed, 9 Jan 2008 23:21:13 +0100, "Enrico Lazzerini"

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Sure. Take any old PC. Hook up it's printer port to the Z80
keyboard entry.
Run some dos version on the PC. Not at all critical which one.
After the > prompt, type:
(note the spaces between Y and C and between : and L)
That should do the trick. At least to show the stuff is working

Your screen would no longer show any characters you type, as they
are redirected to the printer.
The PC will (most probably) issue a SYNTAX ERROR after you hit
the return key. And you cannot type Ctrl-Z (as this will end
redirection to the printer.)

No doubt, some program exists to overcome these limitations.

Kind regards,
Gerard Bok

Re: PS2 encoder to parallel (8bits + strobe signals)

Enrico Lazzerini wrote:
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It might be easier to just find a keyboard from that era.

This is an example. Back in that era, you could buy keyboard
encoder chips with parallel outputs. As described in this document,
the keyboard encoder has row and column signals, and scans the array
of keys on the keyboard, looking for key closures. This particular
encoder has the kind of parallel output you are looking

It will be easier to find one of those old keyboard designs,
than to find a custom device to convert PS/2 (serial clock
and data) to a parallel form. I cannot imagine a large
market for such a design, so you'd need to find a
hobbyist who already has made such a thing, to sell
you one.

Back in the 80's, I built my own keyboard, using the same
technique as is shown in the KBD5 document above. I bought a
"raw keyboard" from a company in the States, then designed
my own PCB to hold the encoder chip. The PCB was the biggest
one I ever made on my kitchen table (because it has to be big
enough to allow all the switch contacts from the keys, to be
soldered to the PCB). The fun part, was threading
the leads from each keyswitch, through the PCB. It took a couple
hours, before the "raw keyboard" could be seated onto the
PCB. (All the keyswitch leads have to be inserted into matching
holes, before the keyboard can be seated on the PCB.)

So you could build your own. I didn't find the project itself
to be very complicated, because the encoder chip does (most)
all of the work.

I see something matching the description here, but this looks
like a membrane keyboard and not separate keys. Still, for $9.95,
it would be a quick way to continue with your project. There is
no way of knowing whether the strobe is positive going, negative
going, or whatever, so even with a basic keyboard in hand, you
still may need to do a bit of electronics to make it work.



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