Control.com - Nerds in Control

We have a problem to serial trasmision from a panel Bejers (master) (http://www.e-terminals.com) and an energy analizer Gavazzi SPT90 DIN (2 slave). The protocol is Modbus RTU from RS232, with a converter 232/485. We check the trasmission with test-software from a pc to SPT90, and it is all ok. We already check the trasmission from the panel to another device Modbus RTU, and it is all ok too. We check with the tecnical office Gavazzi the setting of the modbus protocol Bejers, with all solution. Now we suppose that the Modbus request from the panel is not good for the SPT90. Bejers say that your Modbus protocol is 100% Modicon Modbus RTU standard. Where can i find the specification, and the description of Modbus message? There is something to check in this case? MSB-LSB, addressing type (HEX or DEC), J-bus Modbus, serial setting, number of word for each messagge are already checked.

Check your 232-485 converter.

Black Box makes one with an auto driver enable.
Your converter may not be working when hooked to your master because the master may not be signalling the driver to transmit, usually with DTR or /RTS. Some converters need power from the 232 side and use DTR for power.

Hi

At http://www.modbus.pl you can find Modbus Tester. Using the program You can see the raw frames which are read/write to modbus devices, so you will maybe be able check the problem.

Regards
Andrzej

I think you should check it by steps:
1. check communication cable;
2. confirm all devices and meters's communication parameters, for example: station address, data bits, stop bits, parity, communication baud rate, and so on;
3. check above parameter by modbus test software, for example: commtest, modscan;
4. check all devices and meters's modbus address is unique;
5. connect communication cable, RS485 have data+ and data, confirm your connection.

What is the problem you're having? No response? Error response? Bad CRC on the reply?

Greg

In some cases is necessary to add one to the request or adjust your earth.

ex. if you are requesting for the 40001 register you need to add 1 and request by 40002 try that.

the modbus frame is some like that

request:
first two bytes adress, next two bytes function code, next two register to poll, next two lenght(Number of registers to poll), next two lenght, next two CRC.

regards,