Posted By
MMS
on 2021-07-21
08:34:17
 |  Re: Question: Send and recieve data to UNIX-System with the commodore plus/4
I agree, maybe sending and receiveing packagage via the wifi modm would be fastest method with no wiring.
On the other hand, if own a UNIX workstation :-) , you may try the MAX232 circuits, available for few $.
These small board translate the +4 user port TTL level signals to RS232 compatible ones, and you can set up your own serial port communication with the UNIX.
One example:
https://www.ebay.com/itm/113005736222?hash=item1a4faab11e:g:hP0AAOSwCmFbPyHq
This is the same stuff for C64. Actually it is the same as the RS232 Mouse card 
http://biosrhythm.com/?p=1136
almost all UNIX station should have a serial RS232 connector.
For the protocol (although I think you know better than this )
https://www.cyberciti.biz/hardware/5-linux-unix-commands-for-connecting-to-the-serial-console/
The VIC-1011A could also work (it does the same thing as MAX232, and you should not take care of the wiring) but nowadays those original Commodore cartridges costs a lot.
I think due to a communication protocol bug of 6551 you need to cover/block one of the pins on the user port. (same as for the modems), but I am not 100% sure about that, HW gurus could tell
For C16 and C116 the only option is to create a cartridge with 6526 CIA (slow) or MOS 6551 (fast, with external clock up to 125kbit/s speed), or maybe Motorola 6280. https://en.wikipedia.org/wiki/File:Motorola_Microcomputer_Components_1978_pg11.jpg
Maybe two other useful links:
https://ilkerf.tripod.com/cdoc/rs232-pc.html
https://retrocomputing.stackexchange.com/questions/5202/transfer-files-to-dos-over-serial-cable-from-linux
Let us know how it goes on! We would greatly appreciate playing Fortnite on +4 with external CRAY calculus 
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