Output Assign Module


Posted on Feb 6, 2014

The output assign modules uses a 16V8 GAL for address decoding and enable signal generation. Figure 44 shows the pin assignments for the GAL used in the output assign module. The VHDL code used to generate the GALs is included in the appendices, on page The status of 18 pushbutton switches need to be sensed by the microcontroller. Many methods exi


Output Assign Module
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st for connecting switches to a microcontroller bus. To keep parts count and CPU use down, simple latches are used to latch the status of eight switches at a time. Firmware debouncing routines shall take the place of hardware debouncing techniques. The lack of a multiplexing scheme means less CPU time is wasted in reading in the values of the switches, while the firmware debouncing routines mean fewer components are used on the board. Figure 45 shows the circuit used to achieve these goals. Three of these circuits are present, providing a total of 24 pushbutton inputs. Six of these inputs are used for pushbuttons in the universal user interface and cue stack sections of the control board. Figure 45: Output assign module, momentary pushbutton decoding schematic. The output assign module uses three of these circuits, for a total decoding capability of 18 on-board and 6 off-board buttons. The output assign module contains several LED indicators that need to be controlled by the microcontroller. A simple current-sinking scheme involving 74LS373 octal latches is used, identical to that of the fader module. Figure 46 shows the circuit. The output assign module contains a pair of 7-segment LED displays, controlled by the microcontroller. While it certainly would have been possible to drive the displays in a similar fashion to the bare LEDs present on the same board, this was decided against due to the extra bus ports needed....




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