Thanks for pointing out those articles Garth (I've bookmarked his site, lots of good info in there!), especially the wire-wrap question! Good to see I am not the only one using wirewrap for prototyping. Dr. Johnson theorized a top speed of 33MHz, but I'm sure that was for a complicated system. I've run 16-bit counters inside a spartan 2 @80MHz in the PWA successfully. I paid close attention to bypassing all power pins, but I used a similar but more primitive approach to using power/ground "planes" with 24AWG. They were for a MUCH smaller 100-pin QFP package though...
The idea behind the power bars (I'll call them "bars" from now on since they are not technically planes), is to be able to tap a voltage from a single point. The thicker the wire, the closer you come to that single point, though it may be 5 inches away from the source. With so many power pins and grounds coming out of that beautiful 208-pin monstrosity, not to mention the bypass caps I'll have to wire in, I used the thickest AWG I could get my hands on!
After doing some reading on DCM's (yes I'm only up to Chap 3) in the Spartan 3
User Guide, I realized I am doing a no-no by cascading the voltage regulators (Pg.148). It mentions that if this situation is unavoidable, then every VCCAUX must be bypassed which I was intending to do anyway.
I looked at a
schematic for a Spartan 3 starter board from Digilent. They have the VCCO regulator feeding both VCCAUX and VCCINT regulators. I have changed my wiring to be the same.
Also, I have added one more ground bar underneath the Spartan 3. The 144-pin QFP adapter is right on the bottom edge, but it still fits! I'll edit the last pic soon, as now there are 2 major finalizations.
Today and tomorrow I am off from work, my little hands will be busy! Now thinking about it (typing helps me think clearer), I should wire the power and grounds, then wire in JTAG and see if ISE recognizes the FPGA, before I wire all the bypass cap's. This will give me confidence and potentially save alot of rewiring in case I get double vision and wire a wrong pin. All those cap's are gonna get messy.