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st-one-io / node-red-contrib-s7

A Node-RED node to interact with Siemens S7 PLCs
GNU General Public License v3.0
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Sending string #35

Closed MrBoggi closed 5 years ago

MrBoggi commented 5 years ago

I'm trying to send a string from Node Red to my S-1200 CPU. I have a DB configured with both real, bool and strings defined. Real and bool works og but strings give me an error. 21.1.2019, 13:29:38node: PLC msg : error "TypeError: "value" argument is out of bounds"

PLC node config: image

My plc config: image

My inject node for test: image

What can be the issue here?

gfcittolin commented 5 years ago

Your string seems to be too big. Strings have a single byte on their start to store the max. length, and another byte to store the current length, limiting the size of a string to 0~255 characters.

Also keep in mind that these 2 bytes must be accounted for when calculating the space needed. If you have 256 bytes available (304.0 - 48.0 = 256), then your string can have a max length of 254. Therefore, your tag should be DB600,S48.254.

Another option is to use a char array instead of a string, so you don't have this limitation. But then you have to keep track of used bytes elsewhere, and handle this both on Node-RED and in your PLC program

MrBoggi commented 5 years ago

Well.. That makes sense.. and fixes my problem. Hmmm... Thanks for quick help :)

gfcittolin commented 5 years ago

Great, you're welcome!