Check out www.mcselec.com
It is the home of BASCOM-LT a 8051 BASIC compiler.
There are free demo downloads and application examples available.
One of them is an AT keyboard to RS232
converter based on a AT89C2051 MCU.
This should work with a little modification.
The demo compiles up to 1024 Bytes.
A license for BASCOM is $49.
It's a fun tool to work with and makes programming small projects a breeze.

Good luck
Jan