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gavinying / modpoll

A New Command-line Tool for Modbus and MQTT
https://gavinying.github.io/modpoll
MIT License
84 stars 17 forks source link

Issue specifying <object_type>+<start_address> #29

Closed digispiders closed 8 months ago

digispiders commented 8 months ago

Unless Im missing something, here is whats happening: When preparing the config file, it appears that its pulling an offset in the modbus addresses from the object type, and adding the starting_address value to it. So, if you specify:

poll,holding_register,40001,10,BE_BE
ref,objectname,40001,uint16,r

It throws an error. It appears that it might be adding 40001 from the type=holding_register to the specified address (40001) to be polling at the wrong place. If you specify:

poll,holding_register,1,10,BE_BE
ref,objectname,1,uint16,r

It pulls from 40001 (the first holding_register).

Problem: This conflicts with the documentation: helloysd

Suggested Resolution: Should either pull offset from object_type and be documented as such, or ignore type and only pull from specified start_address. outputwith40001 configwith40001 configwith1 outputwith1

Uploading config files and screen shots to demonstrate.

gavinying commented 8 months ago

@digispiders Firstly, congratulate you have actually retrieved data according to your last screenshot.

As you mentioned, instead of polling start from the standard holding_register address 40001, 

poll,holding_register,40001,10,BE_BE
ref,objectname,40001,uint16,r

you end up with polling start from address 1,

poll,holding_register,1,10,BE_BE
ref,objectname,1,uint16,r

This happens quite often because Modbus is an open protocol, different vendors have their own interpretation on the standard, that's why we have many different variants, e.g. zero-based vs one-based, big-endian vs small-endian, etc. Usually vendors will provide documents/examples to help developers for integration.

In your case, your device vendor is using relative address (offset address) rather than absolute address for data comm.

Hope that helps for clarification.

digispiders commented 8 months ago

Okay. It was a little unclear to me based on the documentation in modpoll + what the manufacturer put out, in combination with my poor understanding of modbus addresses. I assumed that an address was an address, and if an 'offset' to an 'address' was specified (e.g. 1 to 40001), I should call the address (40002) which was probably wrong to assume. Feel to close.