APEM AC3559FILL 键盘, 100 mA, 30 V, 1 x 4, 矩阵, 4
The is a 1 x 4 matrix Key Pad can be interfaced easily to a bi-directional 8-bit port on a microprocessor. The latching functions can be achieved by setting and resetting a flag alternatively when a key is pressed. Lighting the LEDs is almost the opposite of reading the keys. Depending on the complexity of the equipment, one could constantly go round a loop adjusting the ON/OFF status of each LED to the required state, effectively scanning the LEDs.