Remember that '1' we were so frantic to get yesterday?
We can't use it.
The line drivers are not behaving as I had assumed they would. Regardless of whether the Hamsters are putting out a '1' or a '0', the line drivers which receive the signal from the Hamster and send it on to the next level are always at '1'. At first we thought the issue was the crossed wires we found on the PCB (courtesy of the last Hamster team), but upon further review of the line driver documentation (Whoo hoo! More documentation!), I noticed where it said "A and B will be high when the line is inactive." So when the Hamster sends out an unchanging '1', the next stage receives an unchanging '1'. However, when the Hamster sends out an unchanging '0', the next stage receives an unchanging '1'. Since the logic for the next level is looking for the change between '1' and '0' and back again, this is obviously not going to work.
The solution is simple. We have the Hamster send out pulses when it's ready to start collecting data and a '0' (in effect, a '1') when it's ready to stop. We write a pulse detecting process for the next level so it can know the difference.
The two-and-a-half hours we spent yesterday on getting that '1'? Well, the extra familiarity with the Hamster documentation certainly won't hurt…
238 words | February 18, 2005 10:41 PM | Ivory tower