Multisim and Ultiboard

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8bit up-down counter ( 74193 * 2 ) works strangely


Hello, everyone.

There is my situation  (I use MS14) -

I have to make counter that produce 1 pulse every time its outputs equal to 127 (0111 1111).

so I have it done.

It works but , 

- take a look at attached pictures

- It creates an extra pulse, but only when it counts down.

I was thinking that is something wrong with 7430 – but I have made other version of 8input NAND – the same result.

Another thought was – there is something wrong with the model of 74193.

But I have made it as real piece of HW. The same thing – there is that damn extra pulse.

What might be a problem?
Any opinion is very appreciated..

Thanks a lot

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