Looking for help desiginig (simple?) circuit

[Jack B. Pollack]

I am looking for some help designing a circuit, or finding a component that
does the following:

1. I need to be able to set the state of a TTL output H or L to follow its
input (call this output X)

2. If another input momentarily goes H, I need output X to toggle its
state.


I thought a D flipflop would be perfect for this.

I was feeding the output of my circuit into the PRESET on the flipflop to
set its state.

I also wired the flipflop to toggle (-Q to D).
My momentary H from step 2 generates the clock input for toggling.


This was almost exactly what I wanted except the PRESET overrides the toggle
input. I need a circuit that can be set or reset, but the toggle input will
take priority over the set/reset input.


Hope this is clear enough. Any help would be appreciated.

Thanks

 

[Don Taylor]

"Jack B. Pollack" <N@NE.nothing> writes:

1. I need to be able to set the state of a TTL output H or L to
follow its input (call this output X)
2. If another input momentarily goes H, I need output X to toggle
its state.

I thought a D flipflop would be perfect for this.
I was feeding the output of my circuit into the PRESET on the
flipflop to set its state.
I also wired the flipflop to toggle (-Q to D).
My momentary H from step 2 generates the clock input for toggling.

This was almost exactly what I wanted except the PRESET overrides
the toggle input. I need a circuit that can be set or reset, but
the toggle input will take priority over the set/reset input.

Maybe I'm off base here but it sounds like feeding your input to
one side of an XOR and using your pulse alone to drive the D you
have built and the output of the D to drive the other side of the
XOR does what you want. The toggle will have priority then.

This ignores timing glitches, which you haven't mentioned yet.

 

[Rich Webb]

On Fri, 10 Oct 2003 21:01:14 -0400, "Jack B. Pollack" <N@NE.nothing>
wrote:

I am looking for some help designing a circuit, or finding a component that
does the following:

1. I need to be able to set the state of a TTL output H or L to follow its
input (call this output X)

2. If another input momentarily goes H, I need output X to toggle its
state.


I thought a D flipflop would be perfect for this.

I was feeding the output of my circuit into the PRESET on the flipflop to
set its state.

I also wired the flipflop to toggle (-Q to D).
My momentary H from step 2 generates the clock input for toggling.


This was almost exactly what I wanted except the PRESET overrides the toggle
input. I need a circuit that can be set or reset, but the toggle input will
take priority over the set/reset input.


Hope this is clear enough. Any help would be appreciated.

Errr... it's late but you might want to look at burning this into a GAL
chip. The GALs are reasonably priced and the design software is free
(WinCUPL -- see www.atmel.com) but you'll need a burner.

--
Rich Webb Norfolk, VA

 

[John Fields]

On Fri, 10 Oct 2003 21:01:14 -0400, "Jack B. Pollack" <N@NE.nothing>
wrote:

I am looking for some help designing a circuit, or finding a component that
does the following:

1. I need to be able to set the state of a TTL output H or L to follow its
input (call this output X)

2. If another input momentarily goes H, I need output X to toggle its
state.


I thought a D flipflop would be perfect for this.

I was feeding the output of my circuit into the PRESET on the flipflop to
set its state.

I also wired the flipflop to toggle (-Q to D).
My momentary H from step 2 generates the clock input for toggling.


This was almost exactly what I wanted except the PRESET overrides the toggle
input. I need a circuit that can be set or reset, but the toggle input will
take priority over the set/reset input.

---
You may have conflicting requirements in that if your toggle input goes
high momentarily and toggles the output then the sense of the S/R input
will be reversed. If that's not a problem, then this ought to work for
you:


S/R >------------------A
+-----+ EXOR Y--->X
+--|D Q|------B
T>-----|--|> _|
| | Q|O-+
| +-----+ |
+-----------+
__ ___
Assuming an HC74, you can set the initial state with the FF's PR or CLR
inputs, which I haven't shown.

--
John Fields