RUT951 send SMS ModBus register 396 hangs

[sangwine]

I am debugging Ruby code running on a Raspberry Pi under Ubuntu to send an SMS message from an RUT951 using ModBus. Following the instructions on the web page at https://wiki.teltonika-networks.com/view/RUT951_Monitoring_via_Modbus is not usable because the Ruby code hangs in an infinite loop after writing a 1 to ModBus register 396 to initiate the send. As far as I can see using irb, the router does not respond to the query sent to it, so the Ruby code hangs in a loop waiting for a response.

How to reproduce:

1. Write a telephone number and message text to ModBus registers 397 … 406 (I am doing this with a Ruby script, but it could be done with a modbus command as detailed in the above webpage (section Send SMS Message).

2. Issue the command:

modbus write -D -p 502 192.168.1.1 %MW396 1

exactly as given in the webpage. This succeeds in sending the SMS, but it does not return to the command prompt. And the debug output shows only the Tx data:

Tx (15 bytes): [00][01][00][00][00][09][01][10][01][8c][00][01][02][00][01]

3. After recovering from the hang with a few Cntl-Cs, trying a similar write to the next register works OK:

modbus write -D -p 502 192.168.1.1 %MW397 123

Tx (15 bytes): [00][01][00][00][00][09][01][10][01][8d][00][01][02][00][7b]
Rx (12 bytes): [00][01][00][00][00][06][01][10][01][8d][00][01]

So, it seems to me that the write to register 396 fails to respond with an echo of the PDU, causing the Ruby code in rmodbus to sit in a loop waiting indefinitely.

Maybe register 396 is different, and cannot be accessed this way, but I am following the instructions given on a Teltonika web page. Any ideas or suggestions would be welcome.

[Daumantas]

Hello,

Could you try writing the message to register 398 and upwards, and then send the message by pushing “1” to register 397?

Best regards,

[sangwine]

Yes, I have tried writing to registers 398 upwards and pushing ‘1’ to register 397. It fails. The problem is definitely not the register number/address. I can succeed in sending an SMS by writing the phone number and message to registers 397 upwards as the first step. Then I edit the script to remove this step, and just leave in writing a ‘1’ to register 396. This correctly sends the SMS (it is received on my phone), but the code hangs, and only a few ^C will stop it and return to the command prompt. Writing to register 396 immediately after writing to registers 397 upwards causes a broken pipe {EPIPE} error.