Datasheet Confusion

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Current being sourced (leaving a terminal) is designated as being
negative, and current being sunk (entering a terminal) is designated
as positive.

"HI"

can

One thing you should learn early about TTL is that it is a current sink logic family. Ouputs are meant to sinking current to ground.

Since you are dealing with a counter, read about debounce circuits for input conditioning prior to connecting a push button to the clock input.

Also, learn to decouple your power supply by using small capacitors very near the IC power pins.

And finally, an open / disconnected input is not a zero.

On Fri, 4 Aug 2006 19:29:39 -0400, in message , "Bart" scribed:

The minus sign merely indicates direction. Note that the max LO current is

+8.0mA. When dealing with digital TTL circuits, you'll run into the terms "source current" and "sink current." The logic "1" output is typically the "source" state, and indicates that the TTL device must be the source of the current for the node, and the value of 400uA is the max that the gate output node can be expected to deliver. When the device is switched to "0," it can be used as a "ground" or "return" "sink" for a separate source of current somewhere on the node, and the max value is the maximum current that the gate can be expected to pass when so configured. I hope that you can see from this explanation that the current direction will be opposite for each case.

Again, the sign only indicates a direction, and I'm not sure why the data sheets determined which direction should be "-" and which should not. That, at least, is my basic understanding of it. If I've erred on some small point, Phil Allison, our resident keeper of all things CORRECT AND PROPER, will be along shortly to call me a twit and a retard, and fail to help in any way toward correcting the error.

HTH!

"Bart" schreef in bericht news:6fca2$44d3d85d$d8441fe4$ snipped-for-privacy@FUSE.NET...

Bart,

Voltage is measured relative to "common" or "ground". As TTLs are used with

5V power supply and connected to GND and Vcc, voltages are always positive. Currents only flow when an output is connected to an input. Currents also have a direction. Manufacturers ever decided to define a positive current to flow into a terminal no matter what terminal (input or output or even Vcc). So current flowing out of a terminal is considered negative. Schematics of in- and output are on the datasheet (at least on my - Texas - one) and you can check out what happens when an output is connected to an input and the output is driven high or low.

petrus bitbyter

Triggering a counter with a raw pushbutton might be instructive as a way to see contact bounce.

Cheers! Rich

Good point....it won't hurt anything but expect it won't work right either.

Thanks to all that replied. I had the Fairchild and Motorola datasheets that didn't give the schematic for output terminals as did the Texas Instruments one. After reading the replies to my post I have a grasp on it now. Thanks again! This group is terrific. Bart