You have two choices to add a serial port to the Raspberry Pi, either over the GPIO connector or using an external USB-Serial converter. You can distinguish between a hardware and a software handshake depending on whether the handshake uses specific handshake pathways or whether it occurs using special ASCII characters (XON/XOFF) embedded in the data stream.Ī typical RS232 port configuration therefore comprises: Baud rate, the number of data bits (5, 6, 7, 8), the number of stop bits (1 or 2), parity (none, odd, or even), handshake (none, hardware or software).Įxample: The flow of voltage during the transmission of the letter 'B', with the configuration 7 databit/no parity/1 stopbit looks as follows. In addition, both devices can agree on a handshake (flow control), with which they inform each other whether they are ready for the data transfer. However, it is necessary that both devices agree upon the same time duration of a single bit. the data transfer can begin at any time (asynchronous protocol). In the idle state the sending and receiving devices are not synchronized with each other, i.e. The transfer is completed with one or two stop bits. In order to facilitate an error correction, a parity bit may be sent which indicates whether an odd or an even number of bits were set, but the parity bit may also be omitted. Then the data itself follows, including 5, 6, 7 or (usually) 8 bits.
The transfer begins with a start bit, where the receiver calls attention to the pending data transfer. It consists of chronologically transmitted data bytes. The format of the transmitted data is simple. Modern computers no longer have serial ports, however this problem can be easily solved with low cost USB-to-serial adapters. Traditionally the serial interface is still used to connect measurement devices (voltmeters, oscilloscopes, etc.) and to communicate with roboters, modems and microprocessor systems (e.g. The source code of all examples can be downloaded from here.Īlthough Bluetooth, Ethernet, or USB interfaces are commonly used for communication between a computer and peripherals (and I 2C, SPI and 1-Wire for microcontroller systems), the communication over the serial interface (RS-232C) is still widespread.
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