Having studied the datasheets / user guides would like to clarify a few points:
1) The difference between the AD7781(20bit) and AD 7780(24bit) appears to be that in the AD7781 (20bit) 4 empty bits are appended such that the communication length is equivalent. Does this mean that the 24bit is actually more accurate or does it mean that those least significant bits are in any case going to be "noise"? For the purposes of choosing an evaluation board does that mean that the 24bit EVAL-AD7780 is the no-brainer choice?
2) I want to test directly with a Microcontroller and not connect to a PC at all. What are the requirements for an external power supply? Is it possible to route it through the ADP3303 or is that component selected only when the jumpers are set for the USB power source from the PC ? (Part of the purpose of using the board is to check the value added of that component, so I hope so!)
3) Is 5v excitation for the load cell generally preferable over 3v, further increasing the resolution?
4) Are there any C language code fragments for the microcontroller SPI interaction with the AD7780?