How to stop counter after it has reached final count?

I want counter to stop counting again i.e for 4 bit down counter 15-0 and then stop counting(not to start again counting from 15-0).How can I do this?

Put a 4 input OR on the counter outputs (output will go low on terminal count), and put this output, plus the clock input into a 2 input NAND and connect the output to the clock input on the counter.

So, you are disconnecting the current clock from the counter clock input and putting the 2 input NAND gate in between. The other input of the 2 input nand goes to the output of a 4 input OR and the inputs of that are connected to the 4 counter outputs.

This assumes that you are using load to reset the counter to 1111 before the start of the sequence.

Edit - Oops - didn't see the down count, gate logic fixed for down count

Sorry,I didn't get your edit.I tried as per your instruction but again counter doesn't stop counting.I want to make my question more clear.I'm using 74LS193 synchronous counter.My circuit counts down but I need to stop at last count(0).

You'll have to debug it or at least post another image of the updated circuit.

The output of the 4 input OR gate will be one for every counter state except 0. When the counter hits 0, the output of the OR gate goes low. When one of the inputs of the NAND gate is low, the output is always high so once the output or the OR gate goes low, the output of the NAND gate should stop toggling with additional clock pulses.

On the last clock pulse, the clock goes from high to low (the edge that the counter updates on). The output of the counter goes to zero. The output of the OR gate goes to zero. The NAND gate inputs should both be zero which will generate a low-to-high transition on the clock input of the counter.. When the clock input goes high, the NAND gate inputs will be 0 and 1 which will still generate a high output on the NAND gate and there will be no clock transition on the counter. When the clock input goes low again, the inputs of the NAND will return to 0 0 and the output will remain high. This cycle repeats until the counter is reloaded with 1111 to restart the sequence.

Hello Nasib,

I have read the datasheet of 74LS193 and came across the borrow and carry out pins of the IC, you can use these pins to achieve the desired result, for e.g. like you said you want the circuit to disable counting, then you can connect the ~bo pin to the base of the transistor, ~bo pin is an active low pin and it goes low whenever the counter reaches 0. you can disable the clock or display by connecting the collector of the transistor such that it turns off the seven segment display or disables the clock to the counter, depending on your requirement.

Hope this Helps, Cheers!