Electronic potential circuit composed of digital circuits

Figure 4-14 is a preset 16-pin electronic potentiometer circuit composed of digital integrated circuits . It consists of three parts: input
controller. Counters, analog electronic switches and resistor networks can be preset.
    The auxiliary input controller consists of a push button switch and a "two-input four-NAND gate" CD4093 with a Schmitt trigger. Used
to control the input of up and down counting pulses to the counter and the conversion of up and down counting states. Among them, ICIA and ICIB form the addition and subtraction counting
input NAND gate. Iclc.rq is a RS flip-flop. Its output terminal controls the up and down counting
state transition of counter IC3. When it outputs high level, IC3 counts up; when it outputs low level, IC3 counts down. IC2E is a AND
non-inverter, IC2F is a counting full control gate. When the counter reaches the preset number or full position, IC3 outputs a full (carry)
signal to close IC2F and stop the input of counting pulses
    to preset the count. . It is composed of BCD preset reversible counting ICCDt029 and BCD preset number switch. It is used to
receive up and down counting pulses and input preset number b. When the count is full, it outputs a full signal to the input controller.
After receiving the counting pulse, the counter counts up and down and then outputs the BCD code. U/D is the up/down counting state conversion control terminal.
When the level is high, the counter counts up; when the level is low, the counter counts down. The port
    simulates the electronic switch and resistor network. It consists of a single 16-channel analog switch CI, CD4067 and a 16-level resistor network.