SWAP CIRCUIT

PROBLEM TO BE SOLVED: To simplify the constitution and to reduce the size of a bus swap circuit for a serial interface which is used to an LSI. SOLUTION: This circuit includes a swap register 8 which is connected to an internal bus 1 that reads and writes the data between a CPU and a peripheral block. The register 8 uses a swap control signal 9 as its input and when the signal 9 is not outputted, the register 8 stores the data which are outputted to the bus 1. When the signal 9 is outputted, the value obtained by swapping the higher and lower order bits of the data outputted to the bus 1 is stored. Then the stored data are read out via the bus 1. No swap circuit is needed in a serial interface 5 owing to presence of the register 8, so that the scale and the area can be reduced for the swap circuit.