8*8 serial port button matrix

Features of this work:

Supports a maximum I/O port flip speed of 10MHz;

Large number of keys, 64 keys, can be expanded;

Hardware debouncing, no software delay required;

Interrupt mode outputs key press signal to save MCU resources.

This piece has 5 pins:

1.VCC (supports 3.3V-6V)

2.GND (public ground)

3.INT: Interrupt output port. When any button is pressed, it outputs a low level. After the button is released, it returns to high level.

4.CLK: Clock input port, the rising edge is valid; when the button is pressed, the MCU gets the interrupt trigger signal, and the microcontroller outputs a rising edge to CLK, making the keyboard in a readable state. At the same time, the DATA port of the keyboard spits out a bit, and then the microcontroller Then output 15 rising edges to CLK, and the keyboard outputs a total of 16 bits, which is two unsigned char;

5.DATA: Keyboard serial data output pin. In the reading state, a bit is output after each rising edge of the clock.

Fundamental:

The button, resistor, capacitor and 74HC14 form a button debounce circuit. After the button is pressed, a jitter-free signal is output;

74HC165 is responsible for temporarily registering the status of the button (parallel signal) and spitting it out in serial mode on the rising edge of the clock;

74HC30 is responsible for detecting whether a button is pressed. When pressed, the 74HC30 output terminal flips;

The two Schmitt triggers of IC3 (74HC14) and 74HC00 and 74HC74 form a simple state machine. When the button is pressed, the 74HC165 is in the merged state and the button state is read; 74HC74 is reset on the first rising edge of the clock , putting the 74HC165 in the string-out state. The state machine uses the principle of action delay on the rising edge of the D flip-flop. When the first rising edge of the clock comes, the D flip-flop has not yet acted, so the 74HC165 is still in the merged state.