Digital display timing circuit

What is shown is a timing control circuit with a digital display function. Its use of digital display allows people to intuitively understand
  the time process and time margin, and can set the timing time at will.
    In this circuit, IC 1 is a 555 time base circuit, which forms an oscillation circuit with peripheral components. 102 is a preset four-bit binary reversible
counter 74LS193. It, together with R2 and C3, forms a subtraction counter with a preset number of 9. IC3 is a BCD-7 segment latch/shadow code, driver CD4511,
which forms the digital display part with the digital tube IC4. cl, Ri, and RP1 are used to determine the flip time of the oscillation circuit. In order to
keep the charge and discharge circuit of cl independent and complementary, VD1 and VD2 are added to the circuit.
    In the circuit, at the moment when the power is turned on, since the voltage across the capacitor C3 cannot change suddenly, a setting pulse is given to IC2. IC2 is set
to 9. At the same time, the voltage across cl is zero and cannot change suddenly. Therefore, the @ and @ pins of IC1 are low level, and its ⑤ pin outputs high level and provides driving pulses
for the counter
. The IC2@ pin outputs a pulse signal and at the same time outputs a four-bit BCD signal, which drives the digital tube IC 4 through the decoder and drive circuit IC3 .