RS-232 Circuit Summary with CCITT Equivalents
| Pin | Interchange | CCITT	 |  Description 	    | Type | Direction|
| 1   |   AA	    |	 101	 | Protective ground	    | gnd  |   n/a    |
| 7   |   AB	    |	 102	 | Signal or common gnd     | gnd  |   n/a    |
| 2   |   BA	    |	 103	 | Transmitted data	    | data |  To DCE  |
| 3   |   BB	    |	 104	 | Received data	    | data | From DCE |
| 4   |   CA	    |	 105	 | Request to send	    | ctrl |  To DCE  |
| 5   |   CB	    |	 106	 | Clear to send	    | ctrl | From DCE |
| 6   |   CC	    |	 107	 | Data set ready	    | ctrl | From DCE |
| 20  |   CD	    |	 108.2	 | Data terminal ready	    | ctrl |  To DCE  |
| 22  |   CE	    |	 125	 | Ring indicator	    | ctrl | From DCE |
| 8   |   CF	    |	 109	 | Rec'd line sig. detect   | ctrl | From DCE |
| 21  |   CG	    |	 110	 | Signal quality detect    | ctrl | From DCE |
| 23  |   CH	    |	 111	 | Data sig. rate sel DTE   | ctrl |  To DCE  |
| 23  |   CI	    |	 112	 | Data sig. rate sel DCE   | ctrl | From DCE |
| 24  |   DA	    |	 113	 | Trans sig elem timing DTE| time |  To DCE  |
| 15  |   DB	    |	 114	 | Trans sig elem timing DCE| time | From DCE |
| 17  |   DD	    |	 115	 | Rec'r sig elem timing DCE| time | From DCE |
| 14  |   SBA	    |	 118	 | Secondary trans. data    | data |  To DCE  |
| 16  |   SBB	    |	 119	 | Secondary rec. data	    | data | From DCE |
| 19  |   SCA	    |	 120	 | Secondary request to send| ctrl |  To DCE  |
| 13  |   SCB	    |	 121	 | Secondary clear to send  | ctrl | From DCE |
| 12  |   SCF	    |	 122	 | Secondary RLSD	    | ctrl | From DCE |
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