Hello Steve,
The M Series User Manual states that each DIO line has a weak pulldown resistor attached to it, and the NI 622X Specifications lists the DIO line pulldown resistor as 50 kOhm typical, 20 kOhm minimum. I understand that you want to interface the DIO lines of your NI 6229 to a device that operates on 3.3V logic. Are you using the DIO lines of the 6229 as inputs or outputs? If you are using them as digital inputs, you shouldn't have to do anything because it will recognize 3.3V as logic high. If you are using the DIO lines as outputs and wish to output 3.3V to an external device, you will need to reduce the voltage. One way to do this is to use a bus transceiver. For more information on 3.3 Volt logic, I recommend reading the knowledge base article titled 3.3 Volt TTL from Digital Products.
Best wishes,
Wallace F.
National Instruments
Applications Engineer
