LAUNCHXL-F28379D: SPI Data Transfer Size

Sir,

I am using SPI Example on LaunchXL-28379D . In this I am observing 16-bits on the scope

SPI_writeDataNonBlocking(SPIB_BASE, 0xAA);

. In the code , I have Sent  Data= 0xAA which is of 8 bits .so it should require  8 clock cycles to send the data.

But In the scope I am observing 16 clock cycles , and the first 8 clock cycles data are 0's.

I need to send  only 8 bits of data . How can I ?

Please suggest