# Data bus tristate transceiver

1. Jun 18, 2011

### coastalmess

**I asked an admin where to post this topic, because i wasnt sure if it should go in the hw forum or not, and was told to post here.

Hello. I am taking a beginning circuits class this summer and every homework assignment is accompanied by a simple thought provoking essay (about a page). Yesterday, this was our topic:

"Data bus tristate transceiver. What is it? How does it work? Why use one?"

I know what data busses are, and i know what a transceiver is. I assume tristate refers to the outputs on the transceiver, but i dont really understand what it means.

Running a search for permutations of "data bus tristate transceiver" didnt result in anything a lay person could easily understand. Is this a specific type of transceiver, or a generalization of all tristate data busses? I read the Wikipedia but obviously thats no credible source. I guess my issue with the assignment is finding reliable information that isnt overly technical. I was hoping one of the EE's out there could point me in the right direction as to where to start my research. Thank you in advance.

2. Jun 18, 2011

### Studiot

Hello coastalmess, welcome to Physics Forums.

I'm sure you are aware that digital circuitry uses two voltage levels - high and low - to represent the binary numbers 1 and 0.

You may be also aware that it is unwise to connect the ouput to two electronic devices together - you wouldn't, for instance, (I hope) wire both ouputs of your stereo amplifier together at the speaker if you only had one speaker. This would result in apalling distorion at best and a loud bang at worst if you did.

Now to apply this wisdom to digital circuits what to do when you want to switch something on from more than one input? You can expect a (not so loud) bang if you simply connect the outputs of two different sending devices together at the input of your switch.

Enter the tri state sender. This can be in one of three states High (1) low (0) or off (high resistance). In the third state it is unaffected by activity from another sender and the system works.

Hope this helps

3. Jun 20, 2011

### coastalmess

Ah. My professor very briefly discussed that via a picture he drew on the board. Your analogy was pretty helpful though, now it makes much more sense. Thank you