| 摘要 |
PURPOSE:To make a signal into a coding signal to fetch it only if two read-out signal coincide, to correctly fetch the signal anytime apart from switch timing by reading out the coding signal twice in a short time and comparing the two read-out signals. CONSTITUTION:A signal level conversion circuit 2 converts the level of the coding signal (a) transmitted from an external device 1 into a voltage level that the circuit 2 handles by itself. The level-converted coding signal (b) is inputted to a comparator 3. It reads out the signal (b) twice according to a pair of timing pulses (d) from a twice read pulse generator circuit 5, and compares the two read-out signals. If they are coincident, a coding signal (c) is outputted to a data processing part 4. If they are non-coincident, the signals are abandoned, and other signals are correctly fetched anytime apart from the timing of switching the coding signal without using a read signal or a busy signal.
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