How to write and read data using SPI protocol?
why dummy data is used?
Refer this link may its useful for you,
Some devices are require an additional control signal from slave to master, indicating when data are ready. This leads to a 5-wire protocol instead of the usual 4. Such a ready or enable signal is often active-low, and needs to be enabled at key points such as after commands or between words. Without such a signal, data transfer rates may need to be slowed down significantly, or protocols may need to have dummy bytes inserted, to accommodate the worst case for the slave response time.]
The Dummy data is 0x00.If you want to read the data from any slave devices,initially send dummy char to slave(to ready to data or move on to data pointer as first line)then only get the original data s from slave.