Sunday, January 11, 2009


So after talking to Brehob (my advisor) about my initial design, he brought up a bunch of interesting points.

1. I absolutely need to find a way to prototype this before I build my own device. Somehow, I thought I was going to design a PCB, solder it up, and then test after I made it. In retrospect that would be absolutely insane. In our lab, we have a bunch of demo boards from Altera with SD card slots, SDRAM, and expansion headers. I think this will be a good way to get started. I plan to cannabalize my Pinnochio SNES cartridge, desolder the rom, put some wires in place, and interface the demo board to that.

2. The core of my project will be an FPGA/CPLD, but I need to pick a specific model. I totally dismissed the idea of having through-hole parts, but Brehob thinks this might be a viable option with a CPLD. In my mind, CPLD is synonymous with "like an FPGA, but not as powerful", so I am skeptical since I don't have a sense of scale for how many gates my designs will need. Ideally, I would have room to try and emulate some of the special chips found in some game carts. The most complex of which is a core that descends from the 6502, with a bunch of crazy extra stuff. At the very least, it would be nice to emulate some of the simpler chips that weren't full CPUs.

I am still unsure, but I did find these two CPLDs which could be suitable granted that my design would fit on them:

Xilinx XC9572-15PCG84C ($7.35 @ digikey) IC CPLD 72MCRCELL 15NS 84PLCC
- 15ns propogation delay
- 1,600 usable gates
Altera EPM7064SLC84-10 ($15.25 @ digikey) IC MAX 7000 CPLD 64 84-PLCC
- 10ns propogation delay
- 1,250 usable gates
Both have:
- Selectable 3.3v/5v IO
- ISP capability (always handy)
- 68 IO pins
- 84-pin PLCC package. (This isn't technically through-hole, but there are dirt-cheap sockets available that breakout to through-hole pins!)

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