Reading float values

[orkhands]

Hi @drunsinn,

I can confirm that the lib works with iTNC530, 606420 02 SP3 quite nicely!

I am able to retrieve correct sensor values from the PLC memory as indicated by the addresses provided by the inventcom article (e.g. 322 milling head speed in revolutions/minute). Yet, so far I am only able to query Integer values. The machine does provide more sensor data, e.g. the milling head torque in Nm as decimals (at least I can see this from the TNCscope tool).

I do not know the specific PLC memory addresses for these values. So I tried reading all the adresses and interpreting them as float, yet this didn't bring up meaningful values anywhere. Doe you have an idea how I can convert the readouts correctly? So far, I am reading the DWORDs and convert them to floats using

value = con.read_plc_memory(address=x, mem_type=pyLSV2.MemoryType.DWORD,count=1)
flval = struct.unpack('f',value[0:4]) 

To do so, I had to change read_plc_memory() to directly return the payload, otherwise, I wasn't able to dissect plc_values further so that I could extract the raw byte data.

I hope I haven't overlooked something here. Thanks!

[drunsinn]

Hello @orkhands,

thanks for the feedback! I will add your software version to my list :-)

I am sorry to say that as far as i know TNCscope is using the DNC library instead of LSV2. I have done quite a bit of searching and analysis with Wireshark but DNC is quite a bit harder to decode than LSV2 which is for the most part just plain text without any encoding.

On the upside it seems that there is indeed a problem in pyLSV2 in reading from the memory address. Currently it is using the telegram R_MB to read values from memory, on a TNC 640 this has worked just fine and i assumed it would also work on an iTNC as i got good values for everything i checked. This seems to not be the case! After checking again with TNCcmd again I found the command GETVALUE which i always ignored as it has some strict limitations:
Availability: iTNC 530 as of 34049x 03 and 60642x 01 or TNC 640 as of 34059x 01 (only with TNCcmdPlus)
This command uses the telegram R_DP to read values by using some kind of special path like \PLC\memory\M\100.

I created a new branch to try reading via R_DP and it seems to work at least for one value :-) check it out here: data_path
It adds the new function read_data_path(path) which takes a string like TNCcmd. This is not ready yet as i have not been able to figure out the meaning of all the byte values sent and revived. If i have time i will take a look next weekend on what i can figure out. If you are interested you can take a look yourself, Pull requests are always welcome!