Switch contacts may be monitored without pulling them. The apparatus comprises an input port module and up to eight switch reader modules, with 128 switch contacts to each. The input port module has four Z80 PIOs providing a total of eight ports for the switch reader modules, and a S-100 bus to a processor. In each switch reader module, a clock provides a four-phase cycle. An address counter cycles to address the 128 switch contacts. In a RUN mode, the operation is to address a switch contact via a multiplex unit on phase one, load the data into a latch on phase two, the output of the latch being the input of a 128-bit shift register, compare the current and previous states represented by the inputs and outputs of the shift register on phase three, advance the shift register on phase four, and advance the address counter on phase one for reading the next switch contact. During phase three, if the switch contact being addressed has changed state, the comparator generates a strobe pulse which is supplied to the port for the switch reader to initiate an interrupt to the processor. At the same time that a strobe pulse is generated, a scan inhibit command is supplied from the comparator to stop the clock. Data from the address counter and the latch output are supplied via the input port module to the processor. The processor then returns a ready signal to resume the scan. There is also a LOAD mode using 512 (4 X 128) read operations to cycle the clock and load the 128 bits of the shift register.
Patent Application Department of the Air Force
- Pub Date:
- April 1986
- Electric Switches;
- Shift Registers;
- Patent Applications;
- Electronics and Electrical Engineering