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smarmengol / Modbus-Master-Slave-for-Arduino

Modbus Master-Slave library for Arduino
GNU Lesser General Public License v2.1
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how to send a broadcast? #57

Open gicking opened 3 years ago

gicking commented 3 years ago

hello,

thanks a lot for this nice library! I am using it for a (very) simple Modbus master to test a RS485 network. So far all worked well. But now I want to send broadcast messages to all connected slaves, and it seems like nothing is sent (checked with oscilloscope).

Specifically in ModbusRtu.h line 55 mentions u8id=0 is intended for broadcast, but line 546 in Modbus::query() returns immediately if u8id==0.

Do I need to call a different method than query() for sending a broadcast and if yes, which one? For a simple example thanks a lot in advance! Have a great day :-)

gicking commented 3 years ago

FYI, as I have some time pressure I made a quick fix, which seems to work.

change line 546 from if ((telegram.u8id==0) || (telegram.u8id>247)) return -3; to if (telegram.u8id>247) return -3;

and change line 621from u8state = COM_WAITING; to if (telegram.u8id!=0) u8state = COM_WAITING; else u8state = COM_IDLE;

imanfreeman commented 3 years ago

I need broadcast too. However, your changes didn't work for me. I change the line 751 from: if (au8Buffer[ ID ] != u8id ) return 0; to if (au8Buffer[ ID ] != u8id && au8Buffer[ ID ] !=0 ) return 0; and now, the slave accepts 0 id as well. Although, the slave processes all the funcions with this id (for example read holding registers), it returns response error not a valid one. Maybe there is a better and concrete solution.

linjovi168 commented 3 years ago

imanfreeman
It is useful to change this code. Is there a way to cancel the returns response in broadcast ?