Connector - +4 User PortAvailable on Commodore +4 computer.UNKNOWN CONNECTOR at the Computer. | Pin | Name | Description |
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| 1 | GND | Ground | | 2 | +5V | +5 VDC | | 3 | /BRESET | ? | | 4 | P2/CSE | Data 2/Cassette Sense | | 5 | P3 | Data 3 | | 6 | P4 | Data 4 | | 7 | P5 | Data 5 | | 8 | RxC | Receive Clock | | 9 | ATN | Attention? | | 10 | +9V | +9 VAC | | 11 | +9V | +9 VAC | | 12 | GND | Ground | | A | GND | Ground | | B | P0 | Data 0 | | C | RxD | Receive Data | | D | RTS | Request to Send | | E | DTR | Data Terminal Ready | | F | P7 | Data 7 | | G | DCD | Data Carrier Detect | | H | P6 | Data 6 | | I | CTS | Clear to Send | | J | DSR | Data Set Ready | | K | TxD | Transmit Data | | L | GND | Ground |
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