PURPOSE: To vary the reading width regardless of the circuit constitution by defining the transfer length of the data which are transferred for each line as the reading width and completing the transfer of data equivalent to one line when the reading width reaches the set value.

CONSTITUTION: A byte unit is defined when a counter 1 counts 8 pieces of transferred data, and the data equivalent to one byte are transferred by means of an FF 3 for direct memory access DMA transfer. In this case, the DMA transfer length of the data transferred is defined as the reading width (transfer byte number). Then a DMA controller of a computer is initialized again for each line (start, i.e., transmission cycle of START signal). An FF 2 applies the interruption to the computer for each end of the transfer of data equivalent to the DMA transfer length. Then an FF 6 is actuated to reset the counter 1. As a result, the reading width can be varied regardless of the circuit constitution.