# Asynchronous parallel bus between two boards.

Discussion in 'Homework Help' started by mikez, Apr 14, 2013.

1. ### mikez Thread Starter Member

Jan 21, 2013
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0
Hi all,
I have a quick question regarding a problem on a homework assignment that is confusing the heck out of me. Here is the problem:

Two boards are connected through an asynchronous parallel bus consisting of 8 data lines. Assume that the cable is 20 meters long and that the signal travels through the cable at a rate of 5ns/m. The lengths of the data paths differ by at most 0.1m. The input register on the receive side of the bus requires a minimum setup time of 10 ns, and a minimum hold tome of 5 ns.

a) What is the maximum rate (in bytes per second) at which data can be transferred across the bus?

b) Show a waveform illustrating how you arrived at the answer.

To be quite honest I have no idea where to start. No formulas or example problems were shown in the lecture notes. From my researching of websites and wiki's is that I will want to try and find out the transmission rate of the bus. The issue is is that I am not given the exact board to look up the specs for. Do I just assume that it is a perfect wire that I am transferring my data across? Any advice would be greatly appreciated.

2. ### WBahn Moderator

Mar 31, 2012
23,562
7,210
It seems like the question is a bit vague because you don't know how the data capture is affected by the receiver. But, in the absence of anything better, assume that one of the signals in the bus is being used as the clock input for the receiver's registers so use that as a reference. Now, assume that one of the other eight signals is faster by the maximum amount possible and yet another is slower by the maximum amount possible. Work up a timing diagram that shows the worst case transitions and from that figure out how close two rising clock edges can be while still meeting the setup/hold requirements on all lines.

3. ### mikez Thread Starter Member

Jan 21, 2013
47
0
Thanks for the quick reply. I have my timing diagram set up, but now I am wondering how I would figure out what the duty cycle is of my clock that is coming in from the bus.

4. ### WBahn Moderator

Mar 31, 2012
23,562
7,210
It's wonderful that you have your timing diagram all set up. Unfortunately, my crystal ball is on the fritz, so could you post it?