Multiplex extender for discrete i/o devices on a time division network

Abstract

A multiplex extender 26 for permitting discrete I/O devices 34, not individually equipped to decode multiplex channel addresses, to be multiplexed on a time division multiplexed control bus 10. The multiplex extender 26 is connected intermediate the time division multiplexed control bus 10 and a branch line 30 and includes a multiplex channel address decoder 78, a data disconnect switch 82 and a branch line controller 90. The multiplex channel address decoder 78 is selectively programmed to one of the multiplex channel addresses of the time division multiplexed control bus 10. The multiplex channel address decoder 78 produces one or more output signals, each being determined by the multiplex channel address which has most recently been decoded. The data disconnect switch 82, connected in series with a data line of the time division multiplexed control bus 10 and a data line of the branch line 30, either passes or blocks the flow of data between the time division multiplexed control bus 10 and the discrete I/O devices 34 in response to the output signal from the multiplex channel decoder 78. A data latch/repeater 86, also connected to the data line of the time division multiplexed control bus 10, selectively stores data from the time division multiplexed control bus 10 or repeats previously stored data to and the discrete I/O devices 34 A branch line controller 90 transmits the previously stored data from the data latch/repeater 86 to the branch line 30 when the data disconnect switch 82 is blocking data frames from the time division multiplexed control bus 10. The multiplex extender 26 can also incorporate a heartbeat pass-through/repeater 94 for passing a heartbeat pulse to the discrete I/O devices 34 during each data frame.