| 摘要 |
<p>A method and apparatus are disclosed for sending and receiving logic signals responsive to external digital data input and control signals. A reference circuit (10, 22) providing a first and second reference signal is common to the signal generating and receiving circuitry. The signal generating circuitry includes a signal source (12) connected to a transmission line (24) for generating a variable level digital signal, and a reference level adjusting and switching circuit ('RLA/S circuit') (10) which is responsive to the digital data input and the first reference signal. The RLA/S circuit is connected to the signal source for selecting the level of the variable level digital signal and providing a switching signal. The signal source output is thus adjusted and switched so that the signal source generates a digital signal to the transmission line which follows the digital data input at the selected output signal level. The signal receiving circuitry includes a variable input impedance circuit (14) connected to the transmission line which is responsive to the second reference signal for receiving variable level digital signals from the transmission line. It also includes a detecting (14, 16) circuit connected to receive the variable level digital signals from the variable input impedance circuit. The detecting circuit is responsive to the first reference signal and detects logic states of the variable level digital signals as determined by the first reference signal. The detecting circuit also converts the detected logic states into corresponding logic signals of predetermined output levels.</p> |
