MICROINSTRUCTION CONTROL CIRCUIT

摘要

PURPOSE:To improve the yield of manufacture and facilitate external test operation by providing double address control circuits with a circuit which tests normalcy and performs switching to a stand-by circuit automatically. CONSTITUTION:If a fault of a next address generating circuit 10 is detected in automatic switching mode and logic ''1'' is outputted to the 1st fault detecting and holding circuit 63, a generation source for a next address is switched from the circuit 10 to a next address holding circuit 11. The check result from the circuit 10 is inhibited through the operation of AND gates 60 and 61 and an inverting circuit 66 with a ''1'' signal from the circuit 63 and only the check result from the circuit 11 in use is sent to an OR gate 62. The 2nd fault detecting and holding circuit 64 sets its internal latch and outputs a logic ''1'' signal to a signal line 72 only when the logical output level from the circuit 63 to a signal line 71 is ''1'', the input logical level of an inhibiting signal line 70 is ''0'', and the output level of the gate 62 is ''1''.