Eight-way answering machine circuit

Circuit working principle: It consists of IC, a coding switch and a controller.
The coding switch is composed of input terminals A, B, C, D in the IC, diodes and buttons.
To verify whether the encoding switch is correct, just press and hold any button so that it has a positive
level input and see if the digital tube can display the corresponding number. The four
coding lines A, B, C, and D are 1, 2, 4, and 8 respectively. 3 is
obtained by inputting a positive level from l and 2 at the same time, 5 is obtained by 1+4, and 6 is obtained by 2+ 4 is obtained, and 7 is obtained from 1+2 +4
.