Electrical – short miso and mosi pins in 3 wire spi

The "SPI" in your microcontroller stands for "Serial Perpheral Interface", which is an industry standard I/O port originally defined by Motorola. But the "SPI" in the Analog Devices' AD converter stands for "Serial Port Interface", which is not the same as the SPI in your microcontroller. It's Analog's own definition for a digital interface.

Analog has written an application notes on how to communicate with this port. It can be found here:

AN-877 Interfacing to High Speed ADCs via SPI: http://www.analog.com/static/imported-files/application_notes/56755538964965031881813AN_877.pdf

You might be able to use your microcontroller's SPI port for this, at least partly - the Atmel protocol seems at least somewhat compatible with Serial Peripheral Interface. You could connect your microcontrollers MISO port to the Atmel's SDIO port and then bit-bang the instruction header from your microcontroller to the ADC and then use the hardware SPI to read the data. Or you perhaps could connect both MOSI and MISO together in your MCU and use the pin's direction and mode bits (input-or-output, gpio-or-peripheral) to essentially disable the MOSI pin when you're reading data and MISO pin when you're writing data.

1. You use the DDRx register to define the direction of a pin (Data Direction Register). x is the name of the port you are using. Set the relevant bit to 1 for an output, and 0 for an input.

2. Does your mouse have Windows installed on it? No. The same with microcontrollers. They only need the code on them to perform their own task. Why would the slave need the software that runs on the master?

3. SPI is an incredibly simple protocol. The main thing to remember with it is it's full duplex and synchronous. If the slave needs to send data to the master then it is up to the master to request that data - the slave can't just send data at will to the master. Making sure the slave can respond to the SS signal fast enough is also important - you don't want to miss the first bit of the first byte coming in.