This may help, note the schematic, it has basic ASCI RX/TX off of the Max232
One item I've needed on several occasions was an
ASCII keyboard (TTL or RS-323 levels) for a vintage system. While I do have a few
Keytronic serial keyboards with TTL output - they are old and can be "flaky".
I found a pair of products that convert a standard PS/2 keyboard to RS-232 ASCII output
(and can be modified for TTL). In addition, the vendor was very cooperative about
modifying his product to meet the needs of those of us in the vintage computer community.
To be specific, the standard products support baud rates from 2400bps to 115Kbs.
I contacted the owner of the company ("John Ursoleo" <jursoleo at
att.net>) saying that for the vintage systems I was working with, I needed lower baud
rates. John asked me to send my units back - and reprogrammed them to support the
following baud rates: 110, 300, 600, 1200, 2400, 4800, 9600 and 19,200. He sent them back
to me, and I tested them again with the low speed option and they worked great.
The "low baud rate" version of these products can be ordered with the /LB
option.
Here's where to get the products, manuals, etc.:
PS2ADPT
http://www.versalent.biz/seradpt.htm
PS2PRO
http://www.versalent.biz/ps2pro.htm
Note: The standard output of this product is RS-232 voltage levels - but it is easy to
modify them for TTL levels. Doing so voids the warranty - so you are on your own with this
mod.
I have NO financial interest in this recommendation - it's just a good product
I've found useful...
Cheers,
Lyle