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Extra bytes received at RX buffer of UART

Question asked by netra on Nov 22, 2013
Latest reply on Nov 26, 2013 by CHANDRASEKAR KANNIAPPAN

Hi,

 

We have mcf52259 Controller based hardware board and MQX 3.5 OS, which is communicating with external device on RS 485 (MODBUS RTU Protocol).

We have established communication between this device.

we found during reception of data from the external device

one or two extra bytes are getting added to the beginning of the frame sent by that device.

 

We had debugged and concluded that the bytes are getting added inside UART.

We used Scope and concluded that the additional bytes are not added till the RX pin of the Controller.

 

Please do find the packets send and received ( Bold ones are the extra bytes).

Note: This behavior is not consistent and sometimes we are getting correct response continuously.

    

TX:- 01 03 08 34 00 01 c7 a4

RX:-  01 03 02 00 c8 b9 d2

 

TX:-01 03 03 e8 00 06 45 b8

RX:-  5c 01 03 0c 00 40 00 00 00 00 a5 a5 a5 a5 2c ec bd ff

 

TX:- 01 03 03 e8 00 06 45 b8

RX:-  01 03 0c 00 40 00 00 00 00 a5 a5 a5 a5 2c ec bd ff

 

TX:- 01 03 04 b0 00 01 84 dd

RX:-  fb 01 03 02 00 03 f8 45

 

TX:- 01 03 04 b0 00 01 84 dd

RX:-  01 03 02 00 03 f8 45

 

Thanks in advance ,Please reply

Nisha

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