A Question for Verilog experts

[alexh]

I believe that the verilog files within MiniMig are only name and function compatible. They are not pin compatible with the real things.

It would have been a bit of a pain to make them pin compatible (Eurgh, TriStates!) and considering they were going inside a single FPGA it was the right call.

Also MiniMig doesnt have the same clock/bus structure as a real Amiga. It merges the fast and chip RAM buses and doubles the clock rate of almost every sub-block.

It will be cheaper and easier to scavenge parts for some time I think.

[alexh]

I am a little sceptical about this 5v FPGA compatibility issue. I think it is a non-issue. I've seen it quoted in in many MiniMig posts, but if the chip the FPGA is connecting to is TTL 5v (which I think Amiga chips are?) then 3.3v FPGA's will be fine.

I use them in this way at work all the time.

However that is the least of your problems, the functionality of the MiniMig source (to be used for chip replacements) is more of an issue.

[alexh]

All the FPGA inputs I've used have what is described as 5v tolerant I/O and so you can just wire in 5v inputs as normal.

The same applies for 3.3v outputs.

A TTL signal is defined as "low" or L when between 0v and 0.8v with respect to the ground terminal, and "high" or H when between 2v and 5v.

This means that a 3.3v FPGA output should fall within the TTL high voltage range and should just work?

I dont see any need for any extra electronics, but I am not a PCB designer. Our PCB designers here make 3.3v FPGA designs which are just "wired" to 5v TTL chips.

[alexh]

Looking at the spartan 3 datasheet, it doesnt have any 5v tolerant I/O like the virtex FPGA's we use. However there is an APPNOTE on how to make them 5v tolerant with a series resistor.

http://www.xilinx.com/support/answers/19146.htm

Outputs should be fine I think as they are between 2v and 5v for TTL, but dont quote me as I'm not a PCB designer.