Red wire is positive. FC Whits wire is grounded. Red wire is grounded. The above values are the values used by the ROM, except for FC which is not used since the system never sets both wires to ground. Other values can be used, but these gives the best results.
White wire is grounded.
Red wire is grounded. This port is used to read the keypad. When a byte is written to port 1, any bit set will mask out the keys listed below. When the keypad is read,a low bit means that one of the keys listed has been pressed. This register is controlles the speed of the hardware interrupts.