SCSI CONTROLLER

PROBLEM TO BE SOLVED: To reduce overheads and to accelerate an SCSI processing by confirming the phase of SCSI executed before abnormality is developed by reading a register. SOLUTION: An SCSI phase to be executed next is written in the phase write register 111 of a phase sequencer block 11 for writing in a phase. Then, next phase data 14 and a phase clock 15 outputted at the timing of changing the phase are inputted to a phase generation block 12 and the signals of an SCSI bus are changed. At the time, the phase data 14 and the phase clock 15 are inputted also to a phase monitoring block 13 and the phase immediately before execution is stored by a phase monitoring register 131. Then, when it is required to confirm the previous phase so as to reexecute an operation by a target, by reading the phase monitoring register 131 through a microprocessor, the required number of phases are confirmed and an error processing is executed depending on the contents.