[Coco] Bit-Banger Serial as external console?

[Stephen Pereira]

Hello folks,

I’ve been dormant for quite some time on this list and with my CoCo…  

I have a stock CoCo 3 with Zipster’s SDC, and that’s all right now.  As you may recall, a couple (few?) years ago, I modified the Talbot Microsystems Color Forth to work in RAM along with DECB.  I have that running on my SDC, and I’ve been searching around for a project to work on.  All my other vintage computer systems use my laptop computer as an external console.  This allows me to work on programs externally and send them in to the computer system, rather than tediously type them in on the vintage machine.  Not so with the CoCo.  Since the CoCo is an all-in-one system, I have no external console to send my programs in from, as with my other machines.

I would love to add an external console to my CoCo.  I thought this might be a good project to get me back into Forth programming.  I looked around a bit, but I have not found any information on system calls that can be used to perform character input and output via the bit-banger serial port.  I saw in the “Unraveled” book for the CoCo Basic ROMs that the is a ROM call for doing output - quite logical, since this port was used for the printer output port.  But I have not found anything about doing input from that same port.

Since Drivewire uses that port, I know that it can do both output and input.  Can anyone provide me any pointers to information on using the bit-banger serial port?  Any code examples would be appreciated.  My intent is to write up my code in Forth to add an external console.  I can start up normally, then invoke the code to switch to the external console.  I figure that I can use a control-z or something like that as a flag to switch back to the normal console after I’ve sent in my code.

Thanks very much, in advance, for any thoughts, pointers, or advice that you may have to offer.

smp
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Stephen Pereira
Bedford, NH  03110
KB1SXE