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 . 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.