| 摘要 |
<p>A variable impedance circuit for use in an external circuit whereby the impedance may be altered by the external circuit has a plurality of two terminal impedance elements (12) connected in series. A node (42, 43, 55) is provided between each pair of impedance elements in the series chain (40). The first impedance element (13) and the last impedance element (15) in the series chain (40) are connected to terminals (14, 16), at least one of which is accessible for connection to the external circuit. Each of the nodes (42, 43, 55) may be connected to a terminal (18) which is also accessible for connection to the external circuit. An electrically reprogrammed read-only memory (25) stores the identity of the nde connected such that the identity of this node is retained when power is removed from the variable impedance circuit. When power is returned to the circuit, the node which was previously connected to the terminal is automatically reconnected.</p> |
