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korbac said:using a 74ls193, i made it count from 1 to 9, but after 9, it goes back to 0. can someone help me please?
ericgibbs said:Do you mean decode 'A' [#10..... 1010], rather than '9'.
Not if he uses the synchronous version which I think from memory is the 74LS163.ericgibbs said:If he reloads '1' on a '9' decode, that just give a count range of 1 to 8.
That's why I suggested a synchronous load. See the circuit I posted earlier.hjames said:The ugly part of being asynchronous is that when the output is transitioning between 0111 and 1000, there's a chance that the value 1010 or 1001 will appear on the outputs for some amount of time. This would cause the a premature load, causing some counts to be skipped.
The simplest correct workaround I can think of (if hell-bent on using this part) requires another D flip-flop along with the NAND gate for decoding and an OR to gate the /LOAD line. The wrong (but fun way) is to just hack bit 3 to transition slowly with some extra loading![]()
ericgibbs said:hi hjames,
The LS193 is a synchronous counter, not a async/ripple thru counter.
Regards
Eric
But I suggested using the PE which is synchronous.hjames said:It's a synchronous counter, but there's an asynchronous reset line involved, and gating the output of a binary counter is pretty much the perfect example of a glitch generator. If the two wires going to the NAND decoder gate have different lengths, the NAND gate inputs have different capacitive loadings/threshold voltages, or the two counter flip flops have slightly different clock thresholds, or there's enough induced noise in one of the two lines, you have a race condition and an early load.
The chances of it will probably be pretty low considering the edge speeds involved, but it isn't a good idea in any case.
Actually, a ripple counter would probably be (marginally) preferable since it would always transition the lower bit first. The NAND gate would then see
"01" -> "00" -> "10" when going from '7' to '8'.
ljcox said:But I suggested using the PE which is synchronous.