30th September 2003

Plod along Cassidy.

Well, I've discovered a serious lack of good schematic editors that are free to use (never mind those that are free as in freedom).

I've ended up using McCad to enter the schematics, but that has quite a few limitations... I've had to spread the circuit over a number of separate pages, and use some non-standard shorthand ways of showing connections. (Unfortunately their 'approximately' 200 pin limit is detrimentally approximate - it's quite a bit less than that!).

My »provisional schematics are available now, but I haven't been through them with a fine-toothed-comb. (The pin outs for the »CoolRunner XPLA3 chip are for illustration only.)

I haven't updated the VHDL code yet, but you will notice that the framebuffer size has been extended, and that there's the facility to drive a tri-colour LED. This is to allow me to try to make a 8 colour display operating at effectively 25Hz (i.e. operating at 75Hz with three separate red, green and blue frames).

P.S. for any budding designers of schematic capture packages out there, please do some usability testing. (Try and use one of the packages from the big players - like »PADS - and you'll see what I mean - the rest don't even begin to approach it in usability.)

5th September 2003

Supping on nectar.

I've been puzzling over how to switch between the voltages required for VIDH and VIDL on the »Kopin 320M. All of the analogue switches I looked at seemed to have long delays before the signal appeared on the output, and the 320M needs it to occur in less than 70ns.

I think I've come up with a »simple way to get around this problem (there may be a problem with the supplies not being 'stiff' enough though).

Sorry if that sounds a little cryptic - I just wanted to make an entry on the way to sorting things out. (I know that there seems to be a few people checking occasionally about progress - I am doing things :-)