Problem in rs485 communication

[prasanthapplied]

Dear all,  

   I'm using lpc1768 controller with MAX487 chip for rs485 communication. I can receive a data from outside(terminal) properly via RS485. But sending has a problem. While sending it sends a junk data. If i provide a 100 Milli second delay for each byte send it works properly. My controller RTS pin drops some 800mV when connecting to MAX487 chip. I checked that MAX487 chip with PIC16f1937 controller that works fine. I don't know a reason for it didn't work with ARM controller.

    I need to know LPC1768 can support to MAX487 or not?  Please help me to solve my problem.

Thanks & Regards,

Prasanth.

[jeremyzhou]

Hi prasanth R,

Thank you for your interest in NXP Semiconductor products and 

for the opportunity to serve you.

I'd highly recommend you can try this RS485 demo code with your board to check whether it can work well.

how to clear buffer in usart1 lpc1768?
Have a great day,
TIC

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[prasanthapplied]

Hi Jeremyzhou,

            Thanks a lot your response. I already tried that demo code but no use. While sending it sends a junk characters.

Thanks & Regards,

Prasanth

[jeremyzhou]

Hi prasanth R,

Thanks for your reply.

I was wondering if you can these information to dig deeper.

1. The sch of the MAX487 connect the MCU.

2. The wave screenshot of OSC to illustrate the operation of the MAX487

I'm looking forward to your reply.
Have a great day,
TIC

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[prasanthapplied]

Hi jeremyzhou,

    Thanks for your response.

1. I'm using MX-Base Board Rev12. My board didn't have any RS485 communication. I connected that MAX 487 chip externally with my development board.

2. Now i removed that MAX 487 chip. Because i thought MAX487 is 5V chip but our controller is 3.3v. So now i'm using MAX3430 for RS485 communication. It works fine.

Do you think MAX487 cause a problem?

Thanks & Regards,

Prasanth

[jeremyzhou · Accepted solution]

Hi prasanth R,

Thanks for your reply.

Do you think MAX487 cause a problem?

-- Yes, I've gone over the datasheet, I consider the different level of voltage may cause this issue.
Have a great day,
TIC

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Note: If this post answers your question, please click the Correct Answer button. Thank you!
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[prasanthapplied]

Hi jeremyzhou,

       Thanks a lot for your clarification.

Thanks & Regards,

Prasanth