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The "BSX1" TNC

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

When amateur packet radio started in the early 80's two main designs emerged. One was from the Vancouver group using the VADC protocol, using a number based header. The second and now dominant protocal was the AX25 protocol proposed and implemented by the Tuscon group (TAPR group). Their first node controller was based on, IIRC, a 6809 processor and ascociated peripheral chips. At the time (1983/4, I was living in South Africa with very little disposable income. A friend of mine showed me a software based TNC made by GLB electronics. This seemed pretty simple and I set about cloning it with some alterations to fit in with the parts I had available. For memory, I stacked 2K RAM chips. This was a simple Z80 design. It worked. With some simple PC software to buffer the text IO, the interrupt driven text IO was not too much of a problem in disrupting transmission and reception. The firmware available at the time supported VADC and TAPR version 1 protocols. In 1985, I moved to Nottingham in the UK. I found almost zero packet activity. That which was around was based on the Cambridge Packet System running on BBCX microcomputers - I did not have a BBC micro! I therefore decided to produce a small cheap PCB based on the GLB design and licensed the GLB firmware from GLB Electronics. I also set up a Bulletin Board System (BBS) which I had written in FORTH for my Apple ][ PC. This kick-started Packet in the Nottingham area. Herewith follows documentation for "BSX1" TNC as it was known then. About 700 were built between December 1985 and December 1988 when it was superceeded by the BSX2 TNC.

BSX1 Documentation: The documentation as supplied with the PCB. (70k pdf).

Upgrade Documentation: Later Upgrade documentation. (35k pdf).

Component List: Component listing for original BSX1.

Firmware command summary. (30k pdf).

CPU and Logic Circuit Diagram. (40k pdf)

Modem Circuit Diagram. (26k pdf)

ROM and RAM Circuit Diagram (2.5k pdf)

Copyright 2003, G0BSX, Sheffield, UK.