Please, help with the counter 74LS90

[Kasim13]

Hi Guys,

I am a novice in a circuit digital. I am trying to make a simple counter. Just 0 until 9.

I got to do, but something is wrong. The counter starts with a random number. I want thats it starts in 0.

The 74LS90 has own source volt, then the counter starts with random numbers.

I tried many things, but I couldn't  to do it starts in 0.

Please, Anybody helps me?
I don't know what do.

PrintScreen:
http://img401.imageshack.us/img401/1240/counterdecec6.jpg

As I said, I am novice, then if somebody could show the solution in a image or a file .ms9.

Thank you,

[lacy]

Most of the IC's in Multisim (especially counters) seem to come up with random outputs. The only way I have found to cure this is to manually reset the ICs at simulation start. There may be other ways to do this ,but this is the simplest method I could find.

I am going to post a picture of the modified circuit for you to examine. To set this at zero close the switch before activation the simulation and then just open the switch. It will go from 0-1-2-3 and so on.

[lacy]

Just be advised that this resetting method applies only to the simulator. In the real world it porobably wouldn't be necessary. Just keep that in mind if you want to use this technique.

[Kasim13]

My friend, thank you very very very much!

I didn't know what do more.

Thanks for the explantation too. It's was excellent.

More time, thank you.

🙂

Have a nice Sunday
🙂

[kittmaster]

You can also set the simulation option to start all values to zero. That may help start the counter at zero.

[lacy]

I tried Set to Zero as a first option, but the counter still seem to come up with a random number each time it started up. I have noticed this a lot of IC's in Multisim espcially counters and IC's like the 4017. This is how I came up with my technique of manual reset during "power up". I have been using that for a while in my counting circuits. It is the only way I know right now of accomplishing a reset at "power up" This really needs to be fixed. At power up all IC's should be in thier reset state.

[kittmaster]

Maybe an RC component set on the master reset will help during start up might fix it up

Message Edited by kittmaster on 11-25-2007 12:18 AM

[Lodin]

Hello,

I was not sure, so I took a look at the manual. The "old" 74xx90 has no defined state after power up. Most of the (old?) TTL have no one. So the state of the counter is random at power up and you need a master reset for your whole circuit.

In this case MS matches reality.

regards,

Lodin

[Kasim13]

Hi Guys,

I am with other problem. In fact, the same problem.

Now I am doing a timer. I did the seconds (00 until 59).
The counter is working well.
But... one more time I am with problem in starting the counter in zero.

Please, look the image:
http://img444.imageshack.us/img444/7950/counter10cog9.jpg

Just the first counter can be clean. When I tried to clean the second counter too, but I am not successful.

Please, anybody helps me again?

[Lodin]

Hello Kasim13

here are 2 ideas :

1) the 74ls90 has 2 reset inputs (R01 + R02)

2) Self resetting the counter is good. But there is a reason for connecting QA to InB !

+edit:

sorry, maybe the way of 2) is not workung with 74ls90, I should also read the manual

-edit

Take a look at the datasheet :  http://www.cs.smith.edu/~thiebaut/270/datasheets/sn74ls90rev5.pdf  (page 2!)

regards,

Lodin

Message Edited by Lodin on 11-25-2007 01:50 PM