Originally the purpose of the start bit was to allow the motors etc to get started and allow the receiving end to perform any timing corrections. After the start bit there are a variable number, usually seven or eight, data bits, an optional single parity bit, and finally one or two zero stop bits. The width of this start bit sets the transmission speed - all bits are the same width as the start bit. When the device starts to transmit it first pulls the line low to generate a start bit. The line rests high and represents a zero. What matters is that, irrespective of the voltage, the protocol is always the same.įor the moment let's concentrate on the protocol.Īs already mentioned the protocol is simple. This voltage difference is a problem we will return to later. Today's serial communications work at logic, or TTL levels 0 to 5V or 0 to 3.3V. Notice, however, that early serial communications worked between plus and minus 24V and later ones ☑2V. The earliest standards are V24 and RS232. As the electronic device used to work with serial is called a Universal Asynchronous Receiver/Transmitter, the term UART is also often used. It was invented to make early teletype machines work and hence you will often find abbreviations such as TTY used in connection with it. The serial protocol is very simple - it has to be because it was invented in the days when it was generated using electromechanical components, motors and the like. In this article the Raspberry Pi will be used an example, but the software approach works on any machine that runs Linux or Unix.īut first, what is serial? Serial Protocol However, today its most common and important use is in making connections with small computers and simple peripherals. The serial port is one of the oldest of ways of connecting devices together, but it is still very, very useful. Most machines, even very small machines, still have a serial interface somewhere - the Raspberry Pi has two!Ī serial port provides a way of connecting devices together and provides a reasonably fast communication channel that can be used over a larger distance than most other connections such as USB. Many small devices use a serial connection, Find out how easy Linux makes accessing the serial interface.

Programming a serial interface using C is becoming increasingly important as embedded programming for the IoT takes off.

C serial port example on raspberry pi