Strictly speaking, the i.MX53 does not fully support the RS-485 in hardware.
Traditionally the RTS is used to control transfers, since UART activates RTS at
when data is available to transmit, and a UART checks CTS before and during the
transmission of the data. When all data has been transmitted, the UART should
deactivate RTS.
Some issues may occur because of fact, that RTS control bits relate to FIFO
activities, and does not control RTS fully correctly for RS-485. Additional
software is needed to check when all data bits are really sent to line.
Also, there are a lot RS232-RS485 automatic converters. These converters contains
a fast automatic TX enable circuit. Please look at the following :
http://www.rs485.com/pasc24t.html
http://www.tri-plc.com/auto485.htm
http://www.tri-plc.com/documents/inst-auto485.PDF
Have a great day,
Yuri
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