Re: Homebrew STG card

[Jon Elson <jmelson-at-artsci.wustl.edu>]

Paul Corner wrote:

> Hi Matt, Jon, & Chris
>
> I have shied away from gate arrays and programmable logic - the software tools
> and programming hardware has been to expensive to justify. The idea of using
> just one chip for all the digital functions does sound appealing. The other
> alternative would be simulating LS7266 functions with a PIC chip.
> The dissadvantage of going down this route, would be limiting the silicon
> source to whom ever had the files and/or programer.

Well, yes, that is often true.  There are some packages that are less expensive.
I have the Xilinx package at work, but also Protel (my Electronic CAD package)
has a lot of tools for them and other brands.  I have started using the XC95xx
series for general interface control, as well as where the configurable stuff is
really needed.  The programming logic can be reduced to a bare parallel
port.  In fact, I have to do this for one of our reprogrammable units.
Xilinx provides generic source code to program their chips, I just have to
add my code for the port or interface, and it will go to it.

The problem with the PIC is it is a microprocessor, which can only do one
thing at a time.  If the main CPU is talking to it, it could miss an encoder
movement.  You may be able to code around this, so that it samples the
encoder frequently enough, but it would have to be done carefully.

The logic in the LS7266 is really not all that much.

Jon