Conclusion

AN3070

10/12

Doc ID 16312 Rev 1

4

Conclusion

This application note presents two methods for managing the DE signal and guaranteeing

the timing imposed by the RS-485 & IO-link specifications:

●

The first method uses the DMA transmit complete interrupt and the USART transmit

complete interrupt. It is easy to implement, and it leaves the CPU free to perform other

tasks.

●

The second method uses the USART interrupt. It does not require the DMA channel

and so, can be implemented while the DMA is not available becaused used for other

purposes.

Compared to the USART interrupt method, the DMA interrupt method achieves lower DE

signal switching times. So, if DMA is available for data transmission, it is preferable to use it.

The two methods meet the RS-485 & IO-link timing requirement of 230 kbs transfer speed

(bit time = 4.34 µs).