| 摘要 |
PURPOSE:To operate a microprocessor without causing a hang-up state, even in case a data acknowledge signal is not returned from a user side, by providing a shift register and a gate means. CONSTITUTION:A shift register 22 generates a new data acknowledge DTACK signal based on an upper data strobe inversion UDS and a lower data strobe inversion LDS from a microprocessor 10. In case the DTACK signal is not returned from a target 1, an output signal of the register 22 passes through a gate 26 and is inputted to a gate 27. In this case, in the gate 27, the other input inversion DTACK-1 signal is H level, therefore, its output becomes an inversion DTACK-2 signal, and is sent to the microprocessor 10. Also, in an automatic DTACK mode, after the inversion UDS and the inversion LDS become active, the eight cycle portion of a clock is delayed, the inversion DTACK-2 signal is returned to the processor unconditionally, and a hang-up state can be prevented. |
