- #1
Number2Pencil
- 208
- 1
first off I'm not looking for ANYONE to do the work for me, I have already spent 3-4 hours a day for the last 6 days on this and I'm stuck. It should be easy but something screwy is going on...
Here are the project specifications: Using a SN74LS193 TTL IC, (an up/down counter with a dual clock input and a clear), create and counter that counts from 3 to 7 then repeats itself indefinently, FORWARDS or BACKWARDS. There will be a Mode switch for switching between counting up and counting down, as well as a reset switch that resets the counter to 7. The reset must be Synchronous with the clock even though the Load input on the IC is Asynchronous.
So I designed it using logic to control what appears on the Load-Data Inputs (specifically the C input as this determines whether to load a 3 or a 7 in binary), and logic to control when a signal is HIGH. I connect this signal to an active-LOW preset input on a D flip-flop making the preset inactive when it's a 3 or 7, and sending a low through D to the Q output, connecting that Q to the active-low Load of the counter (thus, it's synchronous).
You can look at my poorly drawn schematic for a better picture (maybe).
The problem I'm having is that the LOW sitting on the D input of the flip-flop is NEVER getting sent through to Q during the down count when it's connected to LOAD of the counter (thus, never activating a LOAD to cycle back through the numbers). BUT, if I disconnect the Q output from the LOAD of the counter and place it on a random unused hole on my bread board, it works FINE! Why on Earth is the Load input driving this signal HIGH?
If you're thinking "well your IC could be damaged". I tried using a different one and had the exact same problem!
I'd appreciate any advice on this matter. There are some pictures attached proving this case. I can't prove that the clock is ticking on the Flip-Flops but I can assure you they were. and the D input is LOW on both pictures (it's kind of hidden behind some wires)
thanks
Here are the project specifications: Using a SN74LS193 TTL IC, (an up/down counter with a dual clock input and a clear), create and counter that counts from 3 to 7 then repeats itself indefinently, FORWARDS or BACKWARDS. There will be a Mode switch for switching between counting up and counting down, as well as a reset switch that resets the counter to 7. The reset must be Synchronous with the clock even though the Load input on the IC is Asynchronous.
So I designed it using logic to control what appears on the Load-Data Inputs (specifically the C input as this determines whether to load a 3 or a 7 in binary), and logic to control when a signal is HIGH. I connect this signal to an active-LOW preset input on a D flip-flop making the preset inactive when it's a 3 or 7, and sending a low through D to the Q output, connecting that Q to the active-low Load of the counter (thus, it's synchronous).
You can look at my poorly drawn schematic for a better picture (maybe).
The problem I'm having is that the LOW sitting on the D input of the flip-flop is NEVER getting sent through to Q during the down count when it's connected to LOAD of the counter (thus, never activating a LOAD to cycle back through the numbers). BUT, if I disconnect the Q output from the LOAD of the counter and place it on a random unused hole on my bread board, it works FINE! Why on Earth is the Load input driving this signal HIGH?
If you're thinking "well your IC could be damaged". I tried using a different one and had the exact same problem!
I'd appreciate any advice on this matter. There are some pictures attached proving this case. I can't prove that the clock is ticking on the Flip-Flops but I can assure you they were. and the D input is LOW on both pictures (it's kind of hidden behind some wires)
thanks