Thread Starter

Felix Diaz

Hello everybody,

Can anyone guide me on how to build a simple circuit to connect an AT keyboard
to a serial RS232 port.
Perhaps the names of a commercial device...

Thank You,

I spent a couple of hours web-surfing on this very topic today. You'd think
that keyboard interfaces would be RS-232 level like serial mice, but they're
not. XT keyboards are so old we won't worry about them, and PS2 and USB
keyboards use bus interfaces that are specific to PC's, so we'll restrict our
discussion to the regular 5-pin DIN connectors on an AT style keyboard.

L3 Electronics makes a serial tap for AT-style keyboards which will output the
keyboard keypress codes as RS232 ASCII codes. They're sold through B&B
electronics ( as part number "FA1".

Another is made by Vectra Electronics (, called the "Reverse
Pipe", part number VIP-345.

My application was going from a keyboard into the serial port of an
Allen-Bradley SLC-5/04, so in a week I'll know if this works correctly or not.


Ken Roach
A-B Seattle

Jeff P. LeBlanc

There are several places on the web which have info on the keyboard. Basically it is a series of scan codes with a terminating character. The main
problem with interfacing one to a serial port is that the signal levels are not RS232. There are more along the lines of TTL levels. A simple CMOS-TTL interface should do the job. After that a simple driver to decode the scan codes is all you need.