To reduce the number of the terminals of a semiconductor integrated circuit by sharing a communication terminal and a terminal except for the terminal.

A data terminal DATA and a chip selection/reference voltage terminal CS/REF are equivalent to the communication terminal constituting a bus line. The CS signal of the chip selection/reference voltage terminal CS/ REF is always 'H' and it becomes 'L' only at a moment when data is rewritten. When the chip selection terminal and the reference voltage terminal are shared, D/A output becomes 'L' while the CS signal is 'L'. Namely, the chip selection terminal being the communication terminal and the reference voltage terminal are shared and they are set to be the chip selection/reference voltage terminal CS/REF and therefore the semiconductor integrated circuit incorporating a data communication function, which can reduce the number of terminals, can be obtained in the semiconductor integrated circuit incorporating the data communication function, which is provided with the communication terminal for data communication and which is a three lines-type serial data transfer system.