SG51K 3.6264Mhz clock chip: why are the outputs so flaky?

Yes, a UART is sensitive to frequency. Having as much as 1/2 bit of error at the end of a 10-bit character would be disaster. That's 5% variation.

There are gazillions of circuits out on the web. A 74LS04 is a good choice, as is a 74HCU04 (note the 'U'). A 74HC04 is _not_.

Define "garbage". As long as the overshoot isn't greater than 10% or so of the total then you should be fine, and depending on the shape even larger overshoots should be OK.

How are you measuring this waveform? It sounds like you're driving some pretty long pieces of wire to make things so sensitive to external influences, or you're powering the thing with long wire runs without any bypass caps. Have you looked at your VCC line to the chip? Is it bouncing around? Are you clipping your scope negative probe onto the chip's negative lead? Did you check the connection of your scope's negative probe to make sure it's still good?

Hi, I use these chips, I have had no problem with them. They can inject noise into the supply but a 50nf cap accross the supply pins kills it. Are you sure your using the right frequency? 3.6864 is more usual. If you live in the UK I'll drop a couple in the post for you.

Most of that "ringing" you see is the result of a lack of ground plane and bypassing, I bet.

And you blame the chip? Sheesh.

This is like complaining that my car's transmission must be damaged when in fact the car isn't moving very quick because it's underwater...

Tim.

At those frequencies you need to have a SHORT scope ground lead. Like to the chip's ground pin, ground lead no longer than 6 inches.

And what kind of scope probe are you using? It should be a proper scope probe, not just a coax cable with alligator clips.

Figures

The one of two I saw didnt produce the expected output. But I am going to dig into it seriously tonight ...

I am going to get a picture put up later to show you (using 3.6264Mhz xtal).

But heres the output with the sg51k/sg531p clock chip:

All I know is that ... the ringing on the outputs of that clock chip isnt allow my system to run ...

Now I have a function generator handy that I can tune to the same frequency and it drives my system without a problem.

Scope ... but I confess my experience is limited.

Well the clock portion of the system has been isolated and built on a solderless breadboard ... theres a few jumper wires about.

But my power lines are stable and I have bypass caps

No. Its pretty clean at 4.92v on my DMM. I also checked on the scope's DC selector ... good powersupply

not exactly ... I am clipping it on the power supply's negative line. Buts its all on a common ground

Yes ...

Ill try that

You are right of course .. its 3.6864Mhz ... NOT 3.6264Mhz glitch in the matrix.

thanks. I am all the way in NY :(

I posted a picture of some useful homemade wire probe holders that get rid of the garbage. Simple to make, just a couple minutes, once you have the proper tools assembled. See (abse) alt.binaries.schematics.electronics subject: Curley Q for noise reduction

Mike

you got me!!! I am using the coax type with red and black alligator leads.

I have the better quality cable with 10x written on it. But I have never used it ... never needed to. and of course the BNC to BNC to test the output of my function generator.

Again I am surprised by all this because the SIMPLE 555 can be wired in mere seconds to provide me with a CLEAN clock (on the same solderless breadboard setup with jumper wires) ... although its not at exactly

Tim I cant make the leads too short I need to test this on a solderless breadboard before integrating it into my core system.

Same goes with the bypass caps ... theres just no way to make them shorter on a solderless breadboard.

LOL point taken! I got a lot to learn thats for sure

with it's trimmer adjusted properly to avoid false under/overshoot.