CCS/TMS320F28379D: How to set SPISTE low for all data set

Tool/software: Code Composer Studio

Hi

The  SPI is set to high speed mode. LSPCLK is 200 MHz. SPI_BIT_RATE=8,   Bit rate is 25 MHz.

I am programing a DDS and I need to set SPISTE low, send 40 bits   5x8 bytes and set SPISTE to high as shown  in example sprug73.pdf Fig.1-6

In  my case SPISTE goes 0 before every character  and  1 after  every character .

How can I group a set of 5 bytes  or 40 bits.

Thanks in advance

Oleg