October 2005


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10.13.2005: "Pre-work on project"

Ok, this entry will serve a dual purpose; refresh readers on the hardware portion of the project, and then cover the work done thus far by me (Jeff) while Shom was working on senior lab.

Hardware is responsible for bringing data in, triggering, and sending it to the PC. Those 3 things comprise the scope of the hardware portion of the project.

The work done thus far, has focused on learning how to use the OrCAD design program so I can make a board layout later on in the year.

Ok, for those of you who wanted more of a detailed answer on what the hardware is doing...

The hardware will be bringing in data from 16 lines. The previous year's design will work well as a basic approach, but will need improvement in order to reduce cross-talk between lines, and to have the full 16 line system. At this point, I'm not sure if I'll be using a ribbon cable or not. We'll see later on.

As far as triggering, last year I looked into it, and decided that it was too late in the year to tackle the problem, and a simple solution could be implemented in software so we could get a more or less working prototype. However, this year I will be doing the triggering on the FPGA so that the perposterous amount of data thats being collected doesn't have to be sent across USB. That creates addition design issues that will need to be addressed. Last year's FPGA program will need to be more or less copmletely redesigned to take into account the new task while keeping the speed.

As a result of all that, the way data is sent to the PC will also have to change. Previously a rather handy function written by the Opal Kelly designers was used. This function simply took up to 2047 bytes of data (which at bits per line, and 16 lines, is not very many points), using a FIFO structure, and sent it to the PC when requested. Now, I will have to design my own larger FIFO memory array, and use one of the other more complicated fucntions to send data to the PC.

As far as what I've been working on thus far, I learned more or less how to design simple circuits in the OrCAD program suite. The suite was difficult to work with and it took me a few weeks just to figure out how to even get a one IC circuit in to the program. I still have a few things that I need to figure out, such as how to place non-IC parts in the system (like a ribbon cable mount and mounting holes). I also need to figure out how I will mount the XEM to my designed board and design a power system if its going to be manufactured.

The other work I did, was just planning out what I'll need to be doing, like the stuff I discussed at the beginning of this entry.