CCS/TMS320F28035: TMS320F28035 3-wire SPI configuration issue

Hi,

       I'm using the TMS320F28035's SPI, to get an angle sensor's angle data. The SPI is configured in 3-wire master mode. To read the sensor's data, first configure the SPI to transmit mode, send the sensor's address and command data (16 bytes), then configure the SPI to receive mode, read the sensor's angle data (16 bytes), and then read the checksum status data (16 bytes). During the whole process, the chip select signal(CSN) should be pulled low all the time, but by measuring, the chip select signal, each time the 16-byte transfer is completed, it will be pulled up once. This will not meet the timing requirements of the sensor. How do I configure the SPI so that the chip select signal stays low for the entire period.

This is part of my program and the screenshot of oscilloscope ,the yellow line is chip select signal,the green line is clock signal.

Thanks!