Checksum UDP ? read value from HVAC controller

General
1

Hello,

i have a HVAC controller. want to read values via a UDP port. In the program software of the controller i can monitor a input value and grap with Wireshark the HEX send to the controller. to do this is a lot of work when you want to read a lot of values.. i like to auto create a working string.
this is the string a grap:
0251fc209a000002b5095d55
what i know is the first 2 is the adres of the controller. the point i want to read is 2b509
here is another HEX grap of the same value:
0251fc289a000002b509cef8
is it possible to create an HEX string if you know the adres (02) and the point (2b509)??

image

2

hi, I doubt 2b509 is the full value as it is an odd number of bytes, starting at offset of 7.5th byte in the data 0251fc289a000002b509cef8

It is more likely to be the 7th + 8th bytes (16 bit) e.g. 02b5 (as is circled in your picture)

Anyhow, that's the finer details - for starters, I will show you how you can pick & select any value you want using the buffer parser node...

image
image851×174 13.9 KB

Now i realise that ^ value is potentially not what you expect, but without a specification / manual for your HVAC (e.g. byte swapping?, int?, uint? etc) - I randomly chose 16 bit UINT (big endian)

example flow...

[{"id":"58bdc980.c562e8","type":"inject","z":"c9ca6ac7.25b568","name":"0251fc209a000002b5095d55","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"0251fc289a000002b509cef8","payloadType":"str","x":1220,"y":100,"wires":[["7544a660.fcb0e8"]]},{"id":"816105c6.6e6208","type":"inject","z":"c9ca6ac7.25b568","name":"0251fc289a000002b509cef8","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"0251fc289a000002b509cef8","payloadType":"str","x":1220,"y":140,"wires":[["7544a660.fcb0e8"]]},{"id":"7544a660.fcb0e8","type":"buffer-parser","z":"c9ca6ac7.25b568","name":"","data":"payload","dataType":"msg","specification":"spec","specificationType":"ui","items":[{"type":"int8","name":"address","offset":0,"length":1,"offsetbit":0,"scale":1,"mask":""},{"type":"uint16be","name":"data","offset":7,"length":1,"offsetbit":0,"scale":1,"mask":""}],"swap1":"","swap2":"","swap3":"","swap1Type":"swap","swap2Type":"swap","swap3Type":"swap","msgProperty":"payload","msgPropertyType":"str","resultType":"keyvalue","resultTypeType":"output","multipleResult":false,"setTopic":true,"x":1450,"y":120,"wires":[["309f9087.49213"]]},{"id":"309f9087.49213","type":"debug","z":"c9ca6ac7.25b568","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":1470,"y":160,"wires":[]}]
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