• $029B-RIDBE - The byte index to the end of the receiver FIFO buffer.
• $029C-RIDBS - The byte index to the start of the receiver FIFO buffer.
• $029D-RODBS - The byte index to the start of the transmitter FIFO buffer.
• $029E-RODBE - The byte index to the end of the transmitter FIFO buffer.
• $02A1-ENABL - Holds current active interrupts in the CIA #2 ICR. When bit 4 is turned on means that the system is waiting for the Receiver Edge. When bit 1 is turned on then the system is receiving data. When bit 0 is turned on then the system is transmitting data.

THE USER PORT

The user port is meant to connect the Commodore 64 to the outside world. By using the lines available at this port, you can connect the Commodore 64 to a printer, a Votrax Type and Talk, a MODEM, even another computer.

The port on the Commodore 64 is directly connected to one of the 6526 CIA chips. By programming, the CIA will connect to many other devices.

PORT PIN DESCRIPTION