Abstract: A serial bus system in which frames are sent from a central station to a plurality of substations over a first conductor and information is sent from the substation to the central station over a second conductor. Each transmitted frame contains bits identifying whether it is for address, data or a command. An addressed substation sends a handshake back to the central station by changing the logic level of the second conductor. An address frame contains a bit indicating whether a message is to be written into a register of a substation or read from a register therein. Any substation can interrupt to request service from the central station by changing the logic level of the second conductor if the last command on the first conductor is an unaddress command indicating the end of a message.

Abstract: A field effect transistor that shunts a gain control resistor of an operational amplifier is slowly rendered conductive by charging a capacitor through a gate to source resistor and rapidly rendered non-conductive by a transistor connected in parallel with said capacitor so as to prevent undesired transients in the output of the amplifier when the gain is changed from one discrete level to another.

Abstract: One junction field effect transistor is connected in shunt with an operational amplifier so as to render its gain zero when no voltage is applied to its gate and another junction field effect transistor is connected so as to shunt the output of the amplifier to ground when no voltage is applied to its gate.