1.  Technical Field
The present invention generally relates to a semiconductor integrated circuit with a built-in RAM, and more particularly to a semiconductor integrated circuit (LCD driver) that writes input data into a RAM and drives an LCD based on data read out from the RAM. 
2.  Related Art
In an LCD driver of the prior art, when the number of bits of input data is fewer than that of bits of a data bus with which to input data to be written into a RAM from an MPU, data is allotted to the high bit side lines of the data bus.  FIG.  4 shows the relation between the data bus and data in the LCD driver of the prior art.  Here, the number of the data bus is 8 bits while that of data is 5 bits. 
As shown in FIG.  4, in the LCD driver of the prior art, 5-bit data R4 to R0 are supplied to high 5-bit lines D7 to D3 of 8-bit lines D7 to D0 included in the data bus.  Here, since data corresponding to the low 3-bit lines D2 to D0 is not to be stored in the RAM, it is denoted with an ‘*’ as dummy data. 
However, it may be necessary to provide a RAM with data allotted to the low bit side lines of a data bus depending on a customers' specifications, and also the number of bits of data differs.  Thus, it has been required to change the layout of an LCD driver for each case. 
In light of the above problem, the present invention intends to provide a semiconductor integrated circuit capable of selecting lines of a data bus to which data is input when the number of bits of input data is different from that of bits of the data bus with which to input data to be written into a RAM.