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How to know the last byte is received from UART Receive Buffer

Serkan
Intellectual 800 points
Other Parts Discussed in Thread: TM4C123GH6PM

Hello Community Members

I am currently working on UART communication with RS-485 physical interface. There are 8 different boards as slave in line. We are using Tiva TM4C123GH6PM MCU.

When I communicate independently with boards, there is no problem at all. But when these boards are on same line , I can't handle buffer. I mean for example, Master request is in certain length, and if SLAVE_ID and FUNCTION_CODE is true for me, I response to master. But when other slaves responses to master, these responses come to my RX_Buffer too and  I can't know when I should make rx_index to 0.

Since I can't know when I should make my rx_index to 0, everything goes wrong when one of other slaves response to Master.

As summary when there is only one slave

RX_Buffer[rx_index++] = PLC_Request;

Since PLC_Request is in defined length, I can know that when RX_index is 8 or whatever, Make it 0.

if there is more than slave in line

RX_Buffer[rx_index++] = PLC_Request + Slave_Reponse;

In this case Since I can't know length of slave_response, I can not make RX_index to 0 in correct index.

What should I do in this case ?


Thanks in advance

Serkan

  • 0
    Guru 26105 points

    Hi,

    Serkan said:
    Since I can't know length of slave_response, I can not

    Then you may introduce a byte at the beginning of the packet to hold the number of data bytes which will follows(so you can count them), or, if your data is an ASCII message, choose a terminator character to know when it is received.

    Serkan said:
    if there is more than slave in line

    If so, how do you avoid collision if at least two slaves come to speak? some order is needed also here - maybe a slave should not talk if not previously requested by the master.

  • 0 in reply to Petrei
    TI__Guru**** 244400 points
    Hello Petrei

    Do you think a I2C type access should be called, where the master addresses a slave?

    Regards
    Amit
  • 0
    Guru 10570 points
    You might want to consider implementing an existing protocol rather than inventing your own.

    Robert