Hello everyone,

I'm not sure if this question is suitable for this forum because I'm not using a Siemens device. But I thought someone might help me out, or otherwise point out which other forum I should be going to for this.

I'm trying to retrieve data from an AC/DC transformer (http://www.growatt.co.nl/show-42-588.html datasheet and other technical documentation can be found in English if you scroll all the way down) using Modbus. I stuck an RS485 cable into the device with one end and into my PC through a USB connector with the other. 

I then opened ModScan64 and set it up according to this video https://www.youtube.com/watch?v=STBX1Nc2I0s (COM port 3, baud rate 9600, word length 8, parity none, stop bits 1). But I'm not getting any data despite the poll count going up. I'm also getting an error message that reads "MODBUS message TIME-OUT" (see attachment).

Does anyone have an idea what I'm doing wrong? I also have a siemens LOGO PLC which allegedly is Modbus-compatible. Could the solution be in that?

Hi

Modbus uses normally 8E1. check what is the configuration on the device

you cannot simply poll 100 addresses as you are doing. read only what is configured on the device. 

Thank you for your response. What do you mean by 8E1 and what configuration are you talking about? 

In this document, I saw that the input and holding registers should have thousands of registers, which I presume are data addresses that can be read and displayed in ModScan. Why can I not read them?

Modbus slave devices can fail to reply to requests for many reasons:

1. Serial interface parameters incorrect (buad rate, parity etc.)
2. Incorrect slave adddress in the request. Every slave has a uniqure address, and will only respond to requests that are addressed to it.
3. Wiring issues (such as incorrect polarity) or incorrect interface standard (e.g. RS485 cannot talk to an RS232 network).

However, all this pails into insigificance, as it seems from looking at the spec for the device, it doesn't support Modbus protocol. There is no mention on Modbus in the user manual at all. It says it has an RS485 interface, but that is just an electrical standard. It is not a protocol.