Peter Horlacher, DH1PAX developed a circuit for the FT-100 and FT-817 transceivers to enter the desired QRG via a tiny matrix keyboard in German "Funkamateur" magazine (issue 08/2004, page 823; you'll find the source and the binaries on that page - search for "Frequenzeingabe-Tastatur"). Peter uses an Atmel AT90S2313 micro controller to set the QRG via the CAT interface.

As I bought a used TS-50 in summer 2004 I was interested in controlling this rig via CAT, which is possible as David Steeman found out. So I fired my soldering iron and downloaded a demo version of BASCOM, an IDE for the AT90S2313 to program it in BASIC. The demo version is restricted to 2 kBytes of sizes for the produced binaries, but that's enough for the 2313 as its flash size is only 2 kByte anyway.

Here are my TS-50 sources and binaries.