PURPOSE: To maintain reliability required for the center part of exchange control, to secure required throughput, and to attain small space and low power consumption by making a logic IC into a custom LSI.

CONSTITUTION: This exchange is equipped with a main memory 20 composed of a DRAM, an MPU 13 which issues the read command and write command of data on which a code for error correction is attached, the custom LSI 15 which reads out the data corresponding to the read/ write command, and a means 18 which corrects by detecting the error of the data from the memory 20. Also, the LSI 15 is equipped with a DRAM control circuit, a flag for exchange control, a fault recovery circuit, the control circuit of a DMA used in data transfer between an auxiliary memory device, the address decoder of the MPU 13, a wait control circuit when access for the MPU 13 is performed, and a means which switches internal connection based on whether the MPU 13 is the one of universal 16 bits or universal 32 bits. Therefore, the logic IC is made into the custom LSI.