X.21公頭連接器
X.21母頭連接器
X.21介面定義
| Pin | Name | DTE I/O | Description | Type |
|---|---|---|---|---|
| 1 | Shield |  | Shield | Ground |
| 2 | T (A) |  | Transmit (A) | Data |
| 3 | C (A) | | Control (A) | Control |
| 4 | R (A) |  | Receive (A) | Data |
| 5 | I (A) | | Indication (A) | Control |
| 6 | S (A) | | Signal Timing (A) | Timing |
| 7 | B (A) / unused | | Byte Timing (A) or unassigned | Timing |
| 8 | G | | Ground | Ground |
| 9 | T (B) | | Transmit (B) | Data |
| 10 | C (B) | | Control (B) | Control |
| 11 | R (B) | | Receive (B) | Data |
| 12 | I (B) | | Indication (B) | Control |
| 13 | S (B) | | Signal Timing (B) | Timing |
| 14 | B (B) / unused | | Byte Timing (B) or unassigned | Timing |
| 15 | unused |
X.21交叉線定義
| X.21 | X.21 |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 5 |
| 4 | 2 |
| 5 | 3 |
| 6 | 7 |
| 7 | 6 |
| 8 | 8 |
| 9 | 11 |
| 10 | 12 |
| 11 | 9 |
| 12 | 10 |
| 13 | 14 |
| 14 | 13 |
| 15 |
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