User port
The user port is a freely available interface of many Commodore computers of the 8-bit series, and others. a. to be found on the VC-20 , C64 , C128 , Plus / 4 and the desktop computers from the PET 2001 to the CBM-8000 series .
The user port is integrated directly into the main board of the computer as a board connector. The exact design - including the pin assignment - differs depending on the computer model, so that devices to be connected to the user port are often not interchangeable between the different Commodore computers, even if the plugs look the same on the outside. According to the design philosophy of this computer, only the user port of the C128 is fully compatible with that of the C64.
Interface blocks and ports used:
| CBM | VC-20 | C64 and C128 | Plus / 4 |
|---|---|---|---|
| VIA | VIA | CIA | ACIA |
| Port A | Port B | Port B |
The user port was primarily intended for communication via RS232 (e.g. with a modem ), although external voltage converters were required to set the TTL level of the port (0 V / 5 V) to the RS232 standard level (± 12 V). to implement.
The user port could also be used for other tasks, including:
- Connection of EPROM burners
- Emulation of a Centronics interface
- Connection of measuring devices
- Connection of relay boards for general control tasks
- Parallel data transfer to the floppy disk drive by floppy speeder
- Completion of the computer with a reset button (was not standard on the C64 )
- Connection of an external monitor (with TTL level, for PET 2001 to CBM 8296 )