These characteristics define the entire interpretation of the data stream. When transmitting a character there are other characteristics other than the baud rate that must be known or that must be setup. This means each bit has the duration of 1/9600 of a second or about 100 µsec. Therefore, if the line is operating at 9600 baud, the line can switch states 9,600 times per second. The baud rate is the number of times the signal can switch states in one second.

In other words, how long does the signal stay in a particular state to define a bit. Figure 1 shows a diagram of a what a byte transmission would look like.Īt this point you may want to know what is the duration of a bit. The sequence is repeated for each byte sent. When transmitting a byte, the UART (serial port) first sends a START BIT which is a positive voltage (0), followed by the data (general 8 bits, but could be 5, 6, 7, or 8 bits) followed by one or two STOP BITs which is a negative(1) voltage. (The terms MARK and SPACE are also used to simply denote a negative voltage (1) or a positive voltage(0) at the transmit pin respectively). Note that the serial port can also be forced to keep the transmit pin at a positive voltage (0) and is said to be the SPACE or BREAK state. When no data is being sent, the serial port’s transmit pin’s voltage is negative (1) and is said to be in a MARK state. Whenever the serial port sends a logical zero (0) a positive voltage is effected. Electrically speaking, whenever the serial port sends a logical one (1) a negative voltage is effected on the transmit pin. We will discuss the transmit and receive pin first. The serial port contains a electronic chip called a Universal Asynchronous Receiver/ Transmitter (UART) that actually does the conversion.

The serial port is used to convert each byte to a stream of ones and zeroes as well as to convert a streams of ones and zeroes to bytes.

Every character on this page is actually expressed internally as one byte. A bit is basically either a logical 1 or zero. Today’s computers generally address data in bytes or some multiple thereof. Serial communication is basically the transmission or reception of data one bit at a time.

Qt serial communication