Auxiliary power connector and communication channel control circuit

An auxiliary connector circuit is used within an electronic system (10) which comprises a plurality of removable circuit cards (14, 16, 18, 20, 22, 24, 26) which are mounted within a cabinet (12). Before the circuit card (16) is removed from the cabinet (12), a power cable (44) is connected by means of engaging a plug (46) to a socket (34). When this occurs a DATA OUT ENABLE signal at a line (65) drives three-state devices (86, 88, 90, 92, 94, 96, 98 and 100) to a high impedance state to isolate a memory array (78) from a data bus (102). This high impedance prevents any transients from being transmitted through the data bus (102) when the card (16) is removed from the cabinet (12). After the card (16) is removed from the cabinet (12), the power cable (44) can be disconnected from the card (16) or the card (16) can be tested to evaluate the components mounted on the card (16).