another duplex question

trick000

Well I recently ran into a practice exam question asking what the difference is between a half duplex and full duplex on a 32 bit bus. The correct answer was half duplex only pulls 16 bits at a time while full duplex pulls 32 bits at a time. I'm confused. I would think that:

- half duplex on a 32 bit bus (or any width bus) would use the whole data bus width to pull OR push data

- full duplex would use half the bus width for pulling and the other half for pushing data simultaneously if need be or

- full duplex would be able to use the whole data bus width for pulling OR pushing data if need be

is that clear to anybody? Maybe my mind is just fried.

Bravo5

I have looked everywhere and couldn't find an answer to your question. I'm a noob but it would seem to me that if you have something that runs at half-duplex then it would only use half the bus width. If it used the entire 32 bits then why wouldn't you use full-duplex instead? Like a construction site. They are working on one side of a two lane. One side is being repaved so traffic on one side has to wait till the oncoming traffic clears then they can proceed. If both lanes are open it wouldn't make sense to have traffic go in one direction and then send traffic in another direction. Common sense would dictate you would allow traffic to proceed in both directions if both lanes are open. Did I confuse anybody? I think I confused myself or gave myself a brain hernia...one of the two. Anybody got something to add/counter?

Wyldstar

Yea, that seems backwards to me, too. If the data is able to travel in both directions at the same time (which is the definition of full duplex AFAIK) then it would seem logically impossible for the whole bus width to be used to move data in one direction because those pathways are probably in use for data travelling in the other direction.

<shrug>

Maybe the answer they give is just wrong. Wouldn't be the first time.

- WS

chmars53

Digital computer busses can ONLY send OR receive - never both at the same time. Whether serial or parallel makes no difference. Trying to put 2 different voltage levels on one wire at the SAME TIME will yield ONLY the LOWER voltage. You CAN put two (or more) different analog signals (like FSK or modems, or multi-color light over fiber) on the same wire, since there will be a de-modulator at the receiver.

With most external connections (serial or LAN) you have separate wires for in & out, so half-full is determined by a software setting where you set 'hey I'm going to keep watching the input while I send this, and will interrupt the data flow from memory to send the incoming info to the right IO location' (full) or 'wait until I'm done because I don't care what you do until then' (half).

With the newer LANs (100BaseTX) you have 1 pair out & 1 pair in, doubling the 'throughput', but the half/full duplex rules still apply. 100BaseT4 uses 3 pairs for data, 1 for collisions, and can NOT full-duplex.

Just what 32 bit buss was your question about, anyway?

ghaouf

http://infocenter.cramsession.com/techlibrary/GetHtml.asp?ID=1246&GetDes=&CatID=250

this article talks about buses, read it because it might answer your question

also see
http://infocenter.cramsession.com/techlibrary/default.asp?CatID=250
for more great articles