LPC1518's phenomenon of abnormal about RS485

[shawn_ni]

Hi guys;

    I have some questions of RS485, in using NXP's MCU(LPC1518). Specific as follows:

     We configured the RTS signal to provide an output enable signal to control an RS-485 transceiver(USART_CFG[20] = 1).

      But, we found the phenomenon of abnormal that DE would be Low at Sending Data Operation incidentally.It continue about 6us.

      Could you have some suggestions about it ?

      Thank you very much.

[FelipeGarcia]

Hello Shawn,

You can modify the polarity of the output enable signal using the OEPOL bit in USART_CFG[21].

Have a great day,
Felipe

-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!

- We are following threads for 7 weeks after the last post, later replies are ignored
Please open a new thread and refer to the closed one, if you have a related question at a later point in time.
-------------------------------------------------------------------------------

[shawn_ni]

Hi Felipe;

      Thank you for your suggestion .

      However, the problem still exists(only Low become High).

      I uploaded the detailed waveform pictures for reference.

      Can you  help us analysis this problem again ?

Thank you very much,

Shawn

[FelipeGarcia]

Hello Shawn,

I did some testing on my side using LPCXpresso1549 and I found the following behavior in the RTS signal when transmission is taking place, please see snippet below:

Could you please confirm if this is the same issue you found on LPC1518?

Best regards,

Felipe

[shawn_ni]

Hi Felipe;

      Yes, that's the same issue.(only diffrent in OEPOL bit set)

      And we did the same testing on LPC1751.

     The phenomenon of DE(RTS) is always High When transmission is taking place .

     Waveform figure as below  for reference to you:

     We are looking forward to your advice~

Best regards,

Shawn

[FelipeGarcia]

Hi Shawn,

I am going to ask about this issue internally. This seems to be a design error but I will let you know as soon as I have a response.

Best regards,

Felipe