Multiplexing I/O module

DETAILED DESCRIPTION The invention is embodied in an I/O module that performs external addressing of banks of I/O contacts in addition to coupling I/O data.
The I/O module performs high density multiplexing with a minimum of logic circuitry and without its own processor.
In a preferred embodiment uncoded address information is used to multiplex 24 inputs on the machine/process side of the module to an 8-bit I/O data bus on the processor side of the module, while in a second embodiment 6-bit coded addresses are used to multiplex 256 inputs to the same 8-bit I/O data bus.
The module of the present invention more particularly includes a first latch for coupling a bank address on the I/O bus to the I/O module and a first set of gates for coupling this bank address through a set of address terminals to two I/O banks.
The module also includes sequencing circuitry for generating signals in sequence to selected gates in the first set to couple the bank address to two I/O banks in succession.
Two more latches are provided on the module for coupling data between the two I/O banks and two parallel portions of the I/O bus.
The sequencing circuitry also generates clock signals to these two latches to couple a first group of data bits between one I/O bank and one latch, and to thereafter couple a second group of data bits between the other I/O bank and the other latch.
A second set of gates is connected to the two data latches to complete the coupling of a multibit word of I/O data between the two groups of I/O devices and the I/O bus.
One object of the invention is to provide an I/O module with minimum circuitry to multiplex and demultiplex data associated with banks of contacts.
The input module of the present invention is particularly well-suited to reading groups of thumbwheel switches, where each thumbwheel switch generates BCD coded inputs through four input lines.
The module can also be used to couple binary inputs to the main processor of a digital controller.
Another object of the invention is to use certain of the terminals on an I/O connector as address terminals to provide a matrix of inputs or outputs