| 摘要 |
PURPOSE:To obtain a microprogram control device for permitting only necessary control function corresponding to the purpose of respective microprograms by forming a mode register for holding information indicating whether the control functions of respective fields in a microinstruction are to be invalidated or not to a gate circuit. CONSTITUTION:At the execution of a microprogram, a decoder circuit 40 decides the kind of the microprogram to be executed at present on the basis of a value stored in a mode register 60 and output an instruction to gate circuits 50-52 so that a control signal for an unnecessary field is suppressed. In case a loader microinstruction e.g., a control signal for a diagnosis control field B is suppressed by the gate circuit 51. The gate circuit 50 controls a branch control field A so as to restrict the branching functions of all microprograms stored in a control storage 10. Consequently, runaway due to error or the like of the microprogram is suppressed and a new mode is set up in a mode register 60 in accordance with the change of the mode due to branch.
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