Serial, RS232
Overview
Communication as defined in the RS232 standard is an asynchronous serial communication method. The word serial means, that the information is sent one bit at a time. Asynchronous tells us that the information is not sent in predefined time slots. Data transfer can start at any given time and it is the task of the receiver to detect when a message starts and ends.
Voltages
The signal level of the RS232 signal can have two states. A high bit, or mark state is identified by a negative voltage and a low bit or space state uses a positive value. This might be a bit confusing, because in normal circumstances, high logical values are defined by high voltages also. The voltage limitations are shown below.
| Level | Transmitter capable (V) | Receiver capable (V) |
|---|---|---|
| Space state (0) | +5 ... +15 | +3 ... +25 |
| Mark state (1) | -5 ... -15 | -3 ... -25 |
| Undefined | - | -3 ... +3 |
Achievable distances
| Baud rate | Maximum cable length (ft) |
|---|---|
| 19200 | 50 |
| 9600 | 500 |
| 4800 | 1000 |
| 2400 | 3000 |