Three-state vs. normal ciruit

[John M. (spitzie)]

Hi

I’ve started to read about three-state logic which allows multiple 
circuits to share the same output line or lines, such as a bus.
But I’m not really sure if I’ve understand it correctly?

If I (as a beginner) will do a analyse between….

 A data bus that is connected to four circuits whose three-state outputs 
are connected to the bus.

to

A data bus that is connected to four circuits but with normal logic.

Could I then say that the three-state is much better because:

It’s faster?
It removes the device's influence from the rest of the circuit?
I won’t need so much Material (I can reduce the number of wires)?
If I had the normal logic I had to have one bus on every circuit?

Is this right or have I misunderstood anything?

Is there anything else I've missed if I compare/analyse these two 
circuits?

I would really appreciate an answer (English or German doesn’t matter).

Many thanks

S

[Lothar M. (Firma: Titel) (lkmiller) (Moderator)]

John Moore schrieb:
> A data bus that is connected to four circuits but with normal logic.
What is "normal logic"?

"Usual" busses are of tristate architecture, because in such a bus you 
e.g. have RAMs, E(E)PROMs ... with 16 adress lines, 8 (bidirectional) 
data lines and some control lines. And because you can connect them all 
together, you have one bus and (in your example) four chip enable lines, 
which select the active device.

> Is there anything else I've missed if I compare/analyse these two
> circuits?
Also a tristate bus needs "normal" chip select logic.


Try to sctech your two bus architectures on a sheet of paper and post it 
here.

[John M. (spitzie)]

Hi Lothar

Yes I see that may question was strange and when you explain it, I see 
it doesn’t function in reality. I’m trying to understand the different 
between three-state (with three outputs) and what gates I have to use if 
I don’t what to use three-state?
What I mean with “normal” is a gate with two outputs.

So if I had four gates without three-state and would like to connect 
them, I can’t use a bus.
Then I have to connect them separately?
Can you explain how could I do that, and what’s the difference?

Hmm... I don’t now if it is easier to understand:-( ?

Thanks for taking your time for a beginner.

/John

[Lothar M. (Firma: Titel) (lkmiller) (Moderator)]

John Moore schrieb:
> Hmm... I don’t now if it is easier to understand:-( ?
Indeed, no...  :-/

Give a little less abstract example. Dont say "gates" or "devices" or 
"circuits", but more concrete names for those parts.

Lets look at a usual RAM: you must connet it with a tristate bus, 
because it is designed the way that the data bus is bidirectional...

[John M. (spitzie)]

So if we take the RAM for an example, it is design in a way that I have 
to use a tristate bus.
It can then send information in two directions.

However if I want to sent information in two directions to the RAM and 
lets say we don’t have the opportunity to use a tristate, how would that 
be?
Then I have to draw 16 address lines separately and couldn’t use a bus?