What Is RS-232 ?
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What Is RS-232? RS-232 is a standard electrical interface for serial data communications defined by the Electronic Industries Association (EIA). RS-232 actually comes in 3 different flavors (A, B, and C), each one defining a different voltage range for the on and off levels. The most commonly used variety is RS-232C, which defines a mark bit as a voltage between -3V and -12V and a space bit as a voltage between +3V and +12V. The RS-232C specification says these signals can go about 25 feet (8m) before they become unusable. Two standards for serial interfaces you may also see are RS-422 and RS-574. RS-422 uses lower voltages and differential signals to allow cable lengths up to about 1000ft (300m). RS-574 defines the standard 9-pin PC serial connector and voltages. Besides wires for incoming and outgoing data, there are others that provide timing, status, and handshaking. |
RS-232 | |||
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| DB-25 | |||
| Pin | Description | Pin | Description |
| 1 | Earth Ground | 14 | Secondary TXD |
| 2 | TXD - Transmitted Data | 15 | Transmit Clock |
| 3 | RXD - Received Data | 16 | Secondary RXD |
| 4 | RTS - Request To Send | 17 | Receiver Clock |
| 5 | CTS - Clear To Send | 18 | Unassigned |
| 6 | DSR - Data Set Ready | 19 | Secondary RTS |
| 7 | GND - Logic Ground | 20 | DTR - Data Terminal Ready |
| 8 | DCD - Data Carrier Detect | 21 | Signal Quality Detect |
| 9 | Reserved | 22 | Ring Detect |
| 10 | Reserved | 23 | Data Rate Select |
| 11 | Unassigned | 24 | Transmit Clock |
| 12 | Secondary DCD | 25 | Unassigned |
| 13 | Secondary CTS | ||
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| SGI 9-Pin DSUB Signals | |||
| Pin | Description | Pin | Description |
| 1 | Earth Ground | 6 | DSR - Data Set Ready |
| 2 | TXD - Transmitted Data | 7 | GND - Logic Ground |
| 3 | RXD - Received Data | 8 | DCD - Data Carrier Detect |
| 4 | RTS - Request To Send | 9 | DTR - Data Terminal Ready |
| 5 | CTS - Clear To Send | ||
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