[Coco] Bit Banger Port Signals

[Allen Huffman]

On Mar 30, 2013, at 3:30 PM, Gary Becker <Gary_L_Becker at yahoo.com> wrote:
> I had a question about how the Bit Banger Serial port is being used. The three signals are labeled in the service manual as RS232C OUT, RS232C IN, and CD. How are people using the CD pin? If it was hooked up to a modem, the CD pin would indicate a connection was made by the modem. But since modems are not used much any more, does this pin really make sense? I thought using it for a CTS would make more sense. Is anyone using it for this function? Is anyone using it at all?

This is an interesting question to me. Like many here, my first CoCo was a CoCo 1 with cassette deck. I borrowed a 300 baud acoustic coupled modem from a friend of mine, and I believe I continued to use the bitbanger port until I got in to OS-9 and modems got faster than what the bitbanger could handle (back then).

There were many BBS programs that used the bitbanger and "remote terminal driver" programs that links BASIC screen I/O to the serial port. One of the problems in these early 80s days was that if a user hung up on the BBS, it didn't know it and just sat there until the next caller logged in, and was then using the previous user's login. Some systems knew how to prevent this, but I though I recalled the problem was you just couldn't tell about the status of CD through the bitbanger. Certainly, early remote terminal drivers did not.

I recall someone in Houston actually rigging up a photocell so it was stuck over the "CD" light on his 300 baud smartmodem. He would read it through the joystick port, and could then see if the modem thought there was a carrier that.

With workarounds like that being developed, I guess I had no idea the port even had any use for that pin.

Question for the peanut gallery: Using this modern code, just how fast could the bitbanger go as an interactive terminal? I thought, back in the day, 1200 (or maybe 2400?) was as fast as anyone managed. Ken Johnston of Ultimaterm fame was the first one I was aware of going that fast on the bitbanger...? He also wrote a remote terminal driver that had a nice typeahead buffer, also working at...2400 baud? I'd have to go back and look. Our ShadowBBS program used it, and my Sub-Etha Software partner who wrote it ran his BBS entirely on the bitbanger the entire time he was developing it.

My last modem was 14.4, I think, and by then I had to move up to an RS232 pak.
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