Hi,

I have been working on an assignment for days now. and I am stuck.
I was able to program a CMOS 4516 in Multisim to effectively count up and down without jamming the numbers on the chip.

However now I am trying to use a 74LS190 to count down from zero and It just is not clicking on how to code this chip (in hex) to count down. I was able to get the circuit to count down by jamming the values I wanted to the circuit, but that isn't what I want. I need to utilize the counter.

I have read the data sheet extensively and it just isn't clicking.

the inputs are

~U/D ( i get that it counts down when supplied a 1)
~LOAD
~CTEN
P3
P2
P1
P0

I am not grasping what the hex code needs to be to get this thing working how it is supposed to.

 

"74LS190 to count down from zero"

Perhaps you want to count UP from zero?

 

No, The lab wants us to "count down"

so the display would read
"0"
"F"
"E"
"D"
"C"
"B"
"A"
"9"
"8"
"7"
and so forth.

but my issue is understanding the Hexadecimal code required to input into my word generator.
I get that in order to count down a logic high needs to be on the ~U/D but other than jamming my inputs onto P0-P3 I can't get it to work.

I should be able to put in a certain hex value into my word generator without placing any inputs onto the P0-P3 to enable the count down sequence, but it just isn't apparent as to what I need to plug into the word generator.

 

If the ~U/D and ~Load inputs are high and the -CTEN is low then the counter should count down with a clock input.

 

That is what I thought which would give me a Hex input for my word generator of 60 ; which I assumed would show me the count down, but it just isn't working. and I'm not understanding why.

​

 

Maybe the Multisim model is bogus...

 

Maybe the Multisim model is bogus...

Yea, If only my professors would accept that answer!

 

So post your schematic

 

 

You leave the U/D select floating. That is a BAD IDEA! You need to tell it whether you want it to count up or down. Notice the bar above the U, and no bar above D. This means that in order for it to count up, it should have a LOW logic signal (connected to ground), and to count down it should have a HIGH logic signal (connected to V+). Connect it to V+ and try again.

You also don't have a clock going into the chip, as far as I can tell. How do you expect it to change on a clock input when you don't have the clock input connected to a clock source?

That was just the first thing I noticed, there may be other problems as well.

 

Ahh!!! Thank you so much! didn't even notice that I had U/D floating. no wonder it would work. Thanks (facepalm)

 

What are the parts on the left and right? I am not familiar with those symbols.

 

What are the parts on the left and right? I am not familiar with those symbols.

The left is a word generator, it is a pretty handy tool. You can set a buffer size and input each line of code that you want to analyze.
The right is a logic analyzer. if you open it up when you simulate it creates a graph to show you how your signals relate to one another. If you have multisim they are located on the left with the oscope and other tools!