| 摘要 |
<p>PURPOSE:To simply and accurately detect an undefined instruction by counting the number of cycles necessary for the execution of an instruction and detecting whether or not the counted value of cycles is larger than the number of cycles of an instruction having the largest number of cycles among those defined instructions. CONSTITUTION:A cycle counter 20A is usually provided on a microprocessor including a microcomputer to process the instruction processing time. When an instruction read out of a memory is carried out with the use of the counter 20A, the number of cycles necessary for the execution of the instruction is counted by the counter 20A. Then a logic circuit 20B detects whether or not the number of cycles counted by the counter 20A is larger than the number of cycles of an instruction having the largest number of cycles (the largest processing time of an instruction of the microprocessor, i.e., the maximum number of the counter 20A). Thus, an undefined instruction produced by a malfunction can be accurately detected in a simple circuit constitution.</p> |
