Access Count:

The "BSX2" TNC

---TNC Modems
------2400 bps modem

Once packet radio started taking off, the limitations of my first foray into AX25 with the "BSX1" TNC became evident. It supported AX25 version 1 only and was limited in its IO capabilities. The command set was also "non standard" due to the almost universal acceptance of the TAPR TNC2 command set for BBS and terminal programs. I therefore decided to "clone" the TAPR TNC2. I wanted a smaller simpler board with easy to source components. Once I built my prototypes, others became interested and, as a result, I made the boards available at cost to the amateur community. Some 4500 BSX2 boards were built and it formed much of the networking backbone of the UK packet radio network.

Herewith the BSX2 documentation and diagrams:

Documentation: The Basic "BSX2" Revision 5b documentation. (100k pdf)

Logic and Modem Circuit Diagram. (200k jpeg)

Power Supply and Miscellaneous I/O Circuit Diagram. (128k jpeg)

Layout of components on the PCB. (200k jpeg)

State Machine DCD Modification: Revised instructions, courtesy G4MFX. (200k jpeg)

Copyright 2003, G0BSX, Sheffield, UK.