I bet it takes at least a week for someone to reply to this. My experience with Engineer Zone has been pretty bad.
I want to connect the SPI ports of a couple ADI chips (e.g. AD9117 DAC, AD9649 ADC) to the SPI port of a PIC controller. The PIC and every other SPI port I've seen uses two data lines: SDO for data output and SDI for data input. ADI, however, uses a single SDIO bidirectional data line. Apparently this line acts like an input for part of the SPI message and then may become an output if you're reading data from the ADI device.
What's the recommended way to connect this to a two-line SDO/SDI controller? Use a series resistor between SDO and SDIO, and direct connection from SDIO back to SDI?