Digital I/O Voltage Logic Level Compatibility

[blarivee]

I think the PCI6534 High-Speed Digital I/O board can meet my application needs in terms of being able to transfer the required amount of data at the required speed using an appropriate protocol in which the I/O board interfaces with an FPGA that is collecting data from an ADC. However, the FPGA can only be programmed to handle voltage logic levels up to 3.3 V LVCMOS. From reviewing the specifications of the I/O board, it is 5 V TTL/CMOS compatible. The FPGA would be able to produce sufficient logic levels to drive the I/O board with sufficient noise margin, but I don't think that the FPGA could handle a 5V input from the I/O board on it's I/O pins. The FPGA would be damaged. I would like to avoid placing as much hard
ware on the evaluation board as possible. Are there any application solutions from NI that can circumvent this problem? I am currently looking at other I/O boards to see if they can handle 3.3V compatibility as well as investigating different voltage level translation solutions that can be placed between the I/O board and the FPGA. Thank you for your time and suggestions.

[dhuff]

I see 4 options:
1. Try it with the 6534, and maybe use some resistors in a resistor network or pull up/ pull downs to limit the voltage.(being careful not to blow any ports)
2. Try a 3v to 5v converter chip, the DAQ card does run up to 800mA of current at 5V out to a pin on the connector blocks, you can power the chips off of that.(this would add delays, but at least the would be constant and minimal)
3. Try looking for a DAQ card that is isolated (PCI6527 or equivalent) or one with an external reference input. Some of the NI cards have an external voltage reference pin in the card which would allow you to substitute a 3v reference for the standard 5v.
4. Use an analog output card to run digital. Some of the analog cards will have speed comperable to a fast d
igital one.
The good thing about most NI hardware is that you can use the terminal blocks as a good place to hide extra parts like pull up resistors and such.