Hey. i am designing a designing a modbus communications for the STM32F051C8 using RS-485 interface. I am using LTC1480 chip and will be using this cable: https://www.aliexpress.com/item/PC-...MPPT-Solar-Charge-Controller/32815047857.html.

What I am confused about is why would we require to connect both outputs together through a resistor? Also, how do I know whether the USB cable on the receiving end already has a termination resistor installed to USB adapter or not?

 

hi z321,
Look thru this link for guidance.
https://e2e.ti.com/blogs_/b/analogw...ation-is-necessary-and-how-to-do-it-properly#

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Thank you ericgibbs. Also, considering that I need communication both ways, looking at this picture:

I would need to control and toggle /RE and DE pins. I assume both RE DE set logic HIGH would mean that the device is transmitting and set to logic LOW will mean receiving. Would I require to monitor the status of microcontroller TX to determine how to toggle DE and RE pins?

 

hi,
This link shows a typical transceiver connection.
https://www.arrow.com/en/reference-...-transceiver/0f0f531be125c24aacdde6a960cba1ea

/RE and DE are controlled at both ends of the link by a local MCU.

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But how do I control /RE and DE pins? do I link them to any GPIO pin and ensure that they are set high when transmitting and set LOW when receiving?

 

hi,
Yes, you would use GPIO Output pins on the MCU's to control those lines,
You should also consider how you will detect which 'end' of the link has priority to transmit

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Update: is one end of the link defined as the Master and the other end the 'Slave'.?

 

Thank you.sir. Will do some more research now.