Three and a half digital display counter circuit

Shown is a three and a half digital display counter circuit . The counting display circuit in the circuit consists of CD4553, CD4511 and three common
cathode LED digital tubes. CD4553 is used for counting, and CD4511 is used for decoding. The highest count value of this circuit is "J999".
    When the circuit is powered on, due to the action of the cl and Rt reset circuits, the output terminal of the NOR gate 2 is at a low level. LED1 and LED2 do not emit light, and
the thousand-bit "I" composed of them does not light up. When the circuit count changes from "999" to "000", the @ pin of CD4553 outputs a positive pulse . This
pulse causes the NOR gate 1 to output a low level, and the output end of the NOR gate 2 becomes a high level to turn LED1 and LED2 lights up to display the count, shovel 1000",
thus forming a three-and-a-half-digit counting circuit.