Digi-Mod - Schematic
Digi-Mod Schematic (v1.1)
This is the schematic for the v1.1 PCB which differs in a small way from the prototype v1.0 PCB:
The v1.1 PCB has pull-down resistors on all the gate inputs, whereas the v1.0 PCB has pull-up resistors on gates 1, 4, 5, 7 and was to use the internal weak pull-ups of the dsPIC for gates 2, 3, 6, 8. This proved to be problematic as the 100K input protect resistor is too large to allow 0V to pull the input low when the internal weak pull-ups are enabled. This just means that normalised input sockets or external pull-up (or down) resistors must be used on gates 2, 3, 6, 8 so they are not left floating when not connected. If any of these inputs are not used at all then the internal weak pull-ups can be enabled to prevent them from floating.