The primary and secondary data pins, if enabled by the port configuration, provide a method to increase the data throughput of the serial port. They do not behave as totally separate SPORTs; rather, they operate in a synchronous manner (sharing clock and frame sync) but on separate data.
For Example, When Sport is configured in primary data mode (TXSE = 0), the frame sync will get transfer bit for every single data word. Assume total number of data is 17, so 17 frame sync will get transferred for every 17 data word.
But, When Sport is configured for secondary data mode(TXSE = 1), in single frame sync two data word will get transfer. For the total data length is 17, the first 2 data will transmit through primary and secondary channel for single frame sync.
Same the process continues till 17 data transmission get completed. So, it takes half of the frame sync. For 1st frame sync it will transmit 2 data's and continues so it takes only 9 frame sync to transmit 17 data's.