This is the LED Display Matrix schematic. The matrix was composed of 81 two cathode, common anode Red-Green LEDs. Wiring was designed by pairing LED anodes and cathodes together in a schema for each LED to have is own unique address. Each pinout from the Xplained Mini serves to either sink or source current to a cathode or anode in the matrix while each line is pulled high to VCC. This design allows for a total of 18 pins to be used to sink (ground) or source (power) to activate single LEDs without turning on others, thus enabling numerous unique images to be programmed to the matrix.
The wiring of this matrix created 162 unique addresses for LEDs, an address being composed of one anode and one cathode. These were activated by directly writing to the data direction registers (DDRn) and data registers (PORTn) of the Xplained Mini ATmega328P pinout. The logic for activating the DDRn and PORTn allowed for each pin to act as a sink, source, or high impedance input. This was utilized while programming to set these registers to values that would turn on multiple LEDs as desired for an image.