how to send a broadcast?

[gicking]

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]

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]

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]

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