Some SPI targets, such as display drivers, require an additional signal from the SPIM to distinguish between command and data bytes. This line is called D/CX.
SPIM supports additional signals such as a D/CX output line. The D/CX line is set low for transmitting command bytes and high for transmitting data bytes.
The D/CX pin number is selected using PSEL.DCX. The number of command bytes that precede the data bytes is configured using DCXCNT. Writing to DCXCNT during an ongoing transmission is not allowed.
The following figure shows D/CX in use, where SPIM.DCXCNT=1.