C64 RS232 User Port pinout. Available on the Commodore C64/C128. Software emulated. The signals does not have true RS232 levels. It's TTL level, and RXD/TXD is inverted. It's just the normal User Port, used as a RS232 port. Free service manuals.

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Connector pinout: C64 RS232 User Port

Available on the Commodore C64/C128. Software emulated. The signals does not have true RS232 levels. It's TTL level, and RXD/TXD is inverted. It's just the normal User Port, used as a RS232 port.

pin	name	direction	description	color
A	GND		Protective Ground
B+C	FLAG2+PB0		Receive Data (Must be applied to both pins!)
D	PB1		Ready To Send
E	PB2		Data Terminal Ready
F	PB3		Ring Indicator
H	PB4		Data Carrier Detect
K	PB6		Clear To Send
L	PB7		Data Set Ready
M	PA2		Transmit Data
N	GND		Signal Ground