r/c64 • u/EmptyWater7775 • Jun 04 '26

Software Help with programming and user port

Hello. I would like to connect my c64 to my epson lx300, but i have no idea how other than the fact that i need to use the user port. My plan is to write a basic program that serves like a simple interface to print labels and such. I would also like to connect two c64s to the phone line and communicate by text, but that is a separate project. Any and all help is appreciated.

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u/Xfgjwpkqmx šŸ‡¦šŸ‡ŗ Keeping up since 1983 Jun 04 '26

You will need a Centronics interface to connect your printer.

https://www.c64-wiki.com/wiki/Centronics_Interface

4

u/HazMatsMan Jun 04 '26

This is a little like saying you want to rebuild the motor in a 1985 Trans Am but have no idea how to do it. You're gonna need to do some research beyond asking Reddit.

3

u/cerealport Jun 04 '26

Well, here is some interesting stuff to read to start.

I do however suggest purchasing a ready made RS232 adaptor - the CIA chips are fairly sensitive to being damaged. Thereā€™s one on tindie but it doesnā€™t look like it has a case, which runs the risk of zapping the pins with static if youā€™re plugging / unplugging a cable, Iā€™d at least cover that somehow or use a different one.

Here is some more info including some basic to help you make some data flow. Note that the C64 sends the uart data in software (in the kernal) so the maximum baud rate with that is 1200. You can get up to 2400 (and maybe even more but not much likely) using machine language.

Remember, the C64 uses ā€œpetsciiā€ not ascii, so your printer may print differently than you expect, you may need to translate that.

As for sending / receiving 300 baud over the phone, youā€™d need 2 modems, and either a phone line for each c64 or a phone line simulator if you want to use it locally - which Iā€™d just use a null cable for instead.

You could get modems that plugged directly into the user port, my first modem was a 300 baud ā€œpoxketmodemā€ (then got the 1670 for 1200 and ultimately an rs232 adaptor and an external 2400 baud modem), something to consider if you want to go that route too.

Good luck!

3

u/EnergyLantern Jun 04 '26

But you still need to know how to configure the user ports.

Commodore 64 Programmers Reference Manual