EQUIPMENT AND METHOD FOR CHECKING INSTRUCTION OPERATION CODE

摘要

PURPOSE: To allow a program to judge the validity of an unexecuted instruction in the middle of its execution. CONSTITUTION: This device is provided with a test operation code (TSTOP) previously testing the validity of the instruction before the execution of the desired instruction. The previous testing function is included in the microcode of the execution unit 110 of CPU 100 to set a return value showing one of below-mentioned four states within a program state word. The four states are (1) the desired instruction exists and operable, (2) the desired instruction exists in a computer system but this CPU 100 is not usable (at the time of asymmetry, e.g.), (3) the desired instruction does not exist in this computer system and (4) the OP code of TSTOP is recognized but the existence of the desired instruction can not be recognized. A program judging whether to issue the desired program by issuing a TSTOP instruction 108 is capable of testing this return value.