Andrew Greensted (Modified: 17 June 2008)
Electronics > PC Serial Port

PC Serial Port

Information on the PC Serial Port

• Serial Frame

The table below shows some serial frame specs for different baud rates.

Baud	Bit Width	Frame Width (1 start bit, 8 data bits)	Real Data Rate * (1 start bit, 8 data bits, no parity, 1 stop bit)
4800	208.33us	1875us	480 Bytes/s 0.47 KBytes/s
9600	104.17us	937.5us	960 Bytes/s 0.94 KBytes/s
19200	52.08us	468.75us	1920 Bytes/s 1.88 KBytes/s
38400	26.04us	234.38us	3840 Bytes/s 3.75 KBytes/s
57600	17.36us	156.25us	5760 Bytes/s 5.63 KBytes/s
115200	8.68us	78.13us	11520 Bytes/s 11.25 KBytes/s

* It takes a minimum of 10 bits (1 start bit, 8 data bits, no parity, 1 stop bit) to transfer 8 bits of real data. Real data rate is equal to 1/(BitWidth * 10), or Baud/10.

• stty, Linux Serial Port Setup

stty is a command line tool for setting up the serial port. Below are some examples of use.

Set Baud to 9600, use one stop bits.

> stty -F /dev/ttyS0 9600 -cstopb

Set Baud to 115200, use two stop bits.

> stty -F /dev/ttyS0 115200 cstopb

Set Baud to 115200 and character size to 5 bits (can be 5 to 8). Enable parity, set to odd parity.

> stty -F /dev/ttyS0 115200 cs5 parenb parodd

Set Baud to 115200 and character size to 8 bits. Enable parity, set to even parity.

> stty -F /dev/ttyS0 115200 cs8 parenb -parodd