PURPOSE: To discriminate a DMA answer from an HALT answer by detecting a DMA request signal through a flip-flop and obtaining both signals showing the DMA answer and the HALT answer independently of each other according to the detection output of the flip-flop and the output supplied from a microprocessor.

CONSTITUTION: A DMA request signal of an MC6809 type microprocessor 1 is supplied to a D input terminal of an edge trigger type flip-flop FF2. At the same time, a system clock signal of the processor 1 is supplied to the clock input terminal of the FF2 via an inverter 3. An AND of BA and BS signals of the processor 1 is obtained through an AND gate 4. The outputs of the gate 4 and the FF2 are led to AND gates 5 and 7 as well as to an OR gate 6. Then both HALT and DMA answer signals are led out through gates 5 and 7.