App note from NXP link here (PDF)
This application note describes how to implement RS-485 communication with NXP i.MX RT series EVK, and how to design software based on NXP MCUXpresso SDK. For high-speed RS-485 bus, normally the baud rate is up to 5 Mbps; the interrupt and software polling mode is not practical in such a scenario. DMA and other mechanisms must be adopted based on SDK API.