rtu brodcast not work on 3.1.4 ...

[giorgio foga]

i read the post at gihub about brodcast messages .... but is not possible send brodcast messages in RTU mode to multiple slave.... the slave bring it (ctx = 0) as a normal slave ID so the slave with ctx > 0 not receive the writing messages at all ...

regards
giorgio

[Stéphane Raimbault]

Could you explain what to you mean by normal slave ID (0 is reserved for broadcast).

By reading again, https://github.com/stephane/libmodbus/blob/master/tests/unit-test-client.c#L497

I see the test isn't good because only write operations are allowed in broadcast mode

Extract from http://www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf page 7/44:

No response is returned to broadcast requests sent by the master. The broadcast requests are necessarily writing commands. All devices must accept the broadcast for writing function. The address 0 is reserved to identify a broadcast exchange.

https://github.com/stephane/libmodbus/issues/379

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[giorgio foga]

Sorry, is my horrible english .... I know these (0 is reserved for broadcast) .... but when try to send some write register with ctx=0 nothings happens .... when use ctx=255 (I know.... libmodbus use 255 as normal id) the last slave receive the writing (and last for me is ctx=5), when use ctx=1, or ctx=2 or other id slave on my chain all works perfect .... I try these on 3 plc brand ... same issue... I wrote the post because I was not sure it was a bug ... my post is like a warning to sailors ...
Your link obviusly is right (no response .....) ... I use 3.1.2 .... I must change to 3.1.4??

Regards (and real tanks for your work)
Giorgio

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[giorgio foga]

UPDATE .... actually instead broadcast messages I use sent single messages ... I send them in series to a slave station at a time ... after Stephane answer i try resend it with ctx = 0 .... only one messages .... after 5sec the writing ...

actually I use these snip for make connection ...

    ////////////////////////////// ini of modbus line
modbus_t *ctx = modbus_new_rtu("/dev/ttyUSB0", 115200, 'N', 8, 1);


MyTh::MyTh(QObject *parent, bool bth4) :
    QThread(parent), Stop(bth4)
{
    //Debug per libmodbus
    modbus_set_debug(ctx, false); /* i use true only for test it it seem ok*/
    modbus_set_error_recovery(ctx, MODBUS_ERROR_RECOVERY_PROTOCOL);
    //struct timeval responseTimeout;
    //responseTimeout.tv_sec = timeout;
   // responseTimeout.tv_usec = 20;
    modbus_set_response_timeout(ctx, 2, 20);
    modbus_rtu_set_serial_mode(ctx, MODBUS_RTU_RS485);
    //modbus_connect(ctx);
    if ((modbus_connect(ctx)) == -1) {
         modbus_flush(ctx);}
}

it seems ok ... but not understand these delay on writing act..

regards
Giorgio