| 摘要 |
PURPOSE: To ensure the proper transmission/reception of information by storing the digital state of a communication port signal line during an initial term, comparing the stored digital state with the digital state of the same line during a following term and storing a different 2nd digital value when the state is changed. CONSTITUTION: During a test sequence, Hold-Not and Hold signals on a line 30 and a test signal on a line 36 are kept low and a reset signal on a line 34 is kept high. Therefore, the value of a current data signal on a line 28 is stored in a flip-flop 16 by a first clock pulse on a line 32. At the same time, the low value is stored in a flip-flop 26 in the same 1st clock cycle. When the difference between initial data communication latched in a flip-flop 16 and the following data signal on the line 28 is detected, that high signal is latched in the flip-flop 26 in the next cycle of the clock signal on the line 32. Afterwards, the output of the flip-flop 26 is turned high.
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