Multisim and Ultiboard

cancel
Showing results for 
Search instead for 
Did you mean: 

74ls163 issues

I don't know if anybody else has had this issue but I am working on a school project involving the 74ls163. I hook up the load of the 63 to a seven segment common cathode. Like it is supposed to, it counts to 9 but it doesn't reset properly like it should. Instead it counts to 9 and it shuts off and doesn't reset the count. I was wondering if anybody had a solution quickly because I am failing my class with a c and need help that my stupid teacher won't provide.

 

0 Kudos
Message 1 of 3
(2,498 Views)

It is an issue in your logic, you are loading 16 after 9, instead of zero. See attached picture.

 

 

Message 2 of 3
(2,475 Views)

Hi hamburgerman43,

 

This reply does not satisfy your request for a quick solution (because the circuit was part of your school project roughly a year ago). I'm posting this hoping it will be useful for your future activities and for other users of this forum.

 

I agree with azp7, the issue is not in the stupid teacher.

 

@azp7 wrote:

It is an issue in your logic, you are loading 16 after 9, instead of zero. See attached picture.


To be "more correct" you are loading 15 (1111 base 2) at the rising edge of the clock when the output of NAND gate U6 is low, then the count gets stuck in this value (15). For the real-world circuit, this is after a count of 1xx1 base 2 (9, 11, 13, or 15). There is uncertainty which of those four odd numbers greater than 8 precedes the sticking at 15 because the counter was not initialized. I understand that in your simulation the circuit counts to 9 before failing to reset.

 

The first time Qd and Qa both go high, the output of NAND gate U6 goes low asserting ~LOAD. At the next rising edge of the clock, 15 will be loaded to the counter. Since Qd and Qa are high when the counter holds 15, ~LOAD continues to be asserted and 15 gets reloaded at the succeeding rising edge of the clock. This process repeats every clock cycle resulting to the count getting fixed at 15. If you are using the widespread 74xx TTL BCD to seven-segment display decoder/driver such as 74xx48, 74xx49, or functionally equivalent devices (I can only view the image attached by azp7 not your Multisim circuit), you will have a blank display (in your words, "shuts off") as this is how this devices decode binary 1111 (an invalid BCD code).

 

It's possible that you intend to connect the output of NAND gate U6 to ~CLR. That would make your circuit work but you mistakenly wired to ~LOAD. For this specific application, you can set A, B, C, and D to all 0s. Then, ~CLR and ~LOAD become interchangeable for the role of either clearing or reloading the counter.

 

If the application does not require building the counter based on 74xx163,  the decade counters 74xx162 (sync clear) or 74xx160 (direct clear) can be used instead.

 

 

Best regards,

G. Goodwin

0 Kudos
Message 3 of 3
(2,184 Views)