Voltages:
voltage > 3.0V = 0, low, space
voltage < -3.0V = 1, high, mark
| DB-25 (RS-232C) |
|---|
| Function | Abbrev | Pin |
|---|
| Shield | | 1 |
| Transmit Data | TD | 2 |
| Receive Data | RD | 3 |
| Request To Send | RTS | 4 |
| Clear To Send | CTS | 5 |
| Data Set Ready | DSR | 6 |
| Signal Ground | SG | 7 |
| Data Carrier Detect | DCD | 8 |
| Data Terminal Ready | DTR | 20 |
| Ring Indicator | RI | 22 |
| DB-9 (EIA/TIA 574) |
|---|
| Function | Abbrev | Pin |
|---|
| Shield | | |
| Transmit Data | TD | 3 |
| Receive Data | RD | 2 |
| Request To Send | RTS | 7 |
| Clear To Send | CTS | 8 |
| Data Set Ready | DSR | 6 |
| Signal Ground | SG | 5 |
| Data Carrier Detect | DCD | 1 |
| Data Terminal Ready | DTR | 4 |
| Ring Indicator | RI | 9 |
Wikipedia: RS-232
zytrax: RS-232 Cables, Wiring and Pinouts