what is meant by high impedence output?

It means that the output is nearly disconnected in that case. The function table lists a series of input combinations and in some of then the output (I'm not looking at the data sheet, but just speaking generally here) will be 'tristated.' That means the output is left floating to a large degree. This mode allows other chips which may also have active outputs that are tri-statable to be combined externally.

In the case of a tri-statable buffer, they are preparing it for the case where there may be multiple such buffers sharing the same bus and where only one of them, at most, will have their outputs enabled and active and all the rest will be tri-stated. No two of them (or more) should be active, though. Bad news, then. The tri-stating just "lifts the pins off the bus," so to speak. If this is the only such buffer whose output can be on the bus, you might be able to just stay away from tri-stating it and let it stay active all the time.

Does that make sense?

Jon

Learn how to post links so they don't end up split onto several lines:

it's like disconnecting it from the circuit. this allows you to have another device on the same line. for example an IO Input or Output! so you could have input logic connected to the output logic at the same time. when the output logic is not in the Z state, it will output and the connected input device will simply see it reflected back, when the output device is in hi-Z, this line can now be used for an input and the input logic which is still there will see the value from else where. etc.. i think you get it.

a high impedence circuit has has less current but more voltage, a low impedance path will allow more current but drop less voltage

A "high impedance output" is one that is a "weak ouput"; it cannot impart much "effect" on anything so if you measure it with your voltmeter then, it is possible that it may not be able to drive the needle off its stop so it might read 0V but it might not either e.g. "static electricity" also has a "high impedance".

The opposite of this, a "low impedance output" is a "strong output"; it can impart much "effect" e.g. a car battery.

So without knowing anything about electronics, you could correctly guess that a watch battery will have a higher impedance output than a flashlight battery will have a higher impedance output than a car battery.

The highest sort of output impedance would be... nothing at all.

When a battery is new, its "output impedance" is low. When it gets old its "output impedance" gets higher.

If you temporarily short-out a dry-cell, its output impedance will temporarily go high (as gasses build up inside) and then it will recover its original lower output impedance (as the internal gasses are absorbed).

The slangy term "output impedance" is more of an "output resistance" in these cases.

Without a clear understanding of "ouput/input impedance" you won't get anywhere so you are right to ask - more so than you realise. See Thevenin's (tay-venins) Theorem.

Robin

No it means that if you push it it don't budge. If the pin goes high to 4.8 volts it will only deliver a microamp. to use it you need a follower circuit that gives a big current for a small voltage change.A curent amplifier to make the 1 microamp input into a 100 milliamp output. called a cathode follower. or emitter follower, a darlington pair such as a 2n918 pushing a bcy45 would deliver the goods as a double emmitter folower.

I made the viking possible and pushed apollo so they imprisoed me and chopped me brain out.

go forth and help the brits with their mental problems. They need their brains removed, not workers of course, we do the work you get the money....

go forth and multiply.

Some people won't click on those TinyURL, or similar links because they have no idea what the real URL is. It could easily be to a site that will try to install spyware, or worse on your computer.

That may be true in some cases, but in this case, the OP is talking about a TTL logic part with a "tri-state" output. With such parts, when the output is "tir-stated", or placed in a high-impedance condition, the output of the internal circuit is effectively disconnected from the output pin. The chip does not drive the output either high or low. this type of output allows the outputs of several chips to be connected to a common bus, provided that only one chip has its output enabled (not tri-stated) at a time.