Looking for the right FPGA

Question

Hey all!

Been working a bit in the 8-bit world, especially with the Commodore machines, the 64 and SX-64 and I have noticed there have been some folks out there who have replaced some of the chips with FGPAs. I know I am crazy for thinking this, however, I am curious to see if that can be done. I have never used an FPGA nor VHDL, which seems to be the machine language necessary to make this all work. I was using my one machine the other day and the CIA (complex Interface Adapter) basically blew up and stripped me of the two I had for "just in case." I saw one fellow trying to do such a project more than a year ago, and I feel rather inspired.

For the specs below (off the datasheet) What kind of FPGA would be necessary?

FEATURES · 16 Individually programmable I/O lines · 8 or 16-Bit handshaking on read or write · 2 independent, linkable 16-bit interval timers · 24-hour (AM/PM) time of day clock with programmable alarm · 8-Bit shift register for serial I/O · 2TTL Load capability · CMOS compatible I/O lines · 1 MHz operation

ANd if there is a specific FPGA that meets all this, is there a VHDL development software that's free or do you buy it with said FPGA?

michaelkellett · Answer

You could fairly easily use an FPGA to make a plug compatible 6526 part except for the 5V working. Modern FPGAs don't support 5V IO and the CMOS type parts in small packages don't. There are a few 5V working parts but they aren't real FPGAs. I think your best bet would be to use an FPGA with 3.3V IO and level shifting buffers. This will make it a lot harder to design a board with the 6526 footprint but should work OK. You will need a 40MHz or faster clock on the FPGA to meet timing for a 2MHz 6526 without trying too hard. You need a part that comes in a small enough package but that can be prototyped (so no fine pitch BGA). And this is where I'm stuck - there are Lattice CMOS ICE series parts in 48 pin packages but not quite enough IO for you - probably the best bet if you want plug in compatible board but will need buffer and latching trickey Lots of parts in BGA or 144 pin TQFP. If you don't mind the bad footprint then 144 pin TQFP lets you use Lattice ICE40 or XP2 or Altera MAX10. If no other considerations I would suggest the Altera MAX10. Software for any of them is free. MK

johnbeetem · Answer

You might look into the original Xilinx Spartan II (not the IIE). The Spartan II is a 2.5 V internal device with 5V tolerant I/Os if you use 3.3V LVTTL standard. It's an old family but some parts are still available. You'll need to use an older version of the Xilinx tools, but those are available for free at the Xilinx site.

Looking for the right FPGA

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