Hi there,

I've been trying to communicate with the LOGO 8! via modbus using a software that I saw someone using in this forum, but I've been unsucessful at reading a specific VM address.

I'm attaching two pictures to this post in order to show what I'm able to do. I would like to access VM address 60 through the holding register with the address 2, but what I'm actually able to read/write are the VM mapping positions, as seen in the other screenshot.

When using a Float/Integer converter with VM address = 60, using 60 as the starting register in the tester software doesn't write the value on the block. What am I missing ?

Thanks,

Luís

Hello

when you write data from logo to HR register 1001 data is realy write to register HR 1000 in our modbus drive.

Franta M

lmagalhaes

But as you can see in the screenshot, I'm trying to read register 21 (which I was guessing was VW21) and it's actually reading the variable with ID 21 - the ON time of the weekly timer - which is at VW40. So how can I read a variable at VW60 and not in this table?

Careful - the address numbering used by the Modbus addresses vs. the V-memory.

V-memory is byte based and start at zero. Modbus is word based and start at 1.

Source #1:

Source #2:

The PDF shared by ixo65 is very helpful so you do not need to worry for understanding the informations provided with LogoSoft.

BR

Thank you for the PDF, it was very enlightening. However, for the Float/Integer conversion block it has VM and not VW. With the PDF I was able to modify VW values, but still can't figure out the translation from VM to Modbus register address.

If I set the Float/Integer to VM.60, what is the modbus address register that needs to be changed in order to send a float to the logo ?

Thanks,

Luís

lmagalhaes

Thank you for the PDF, it was very enlightening. However, for the Float/Integer conversion block it has VM and not VW. With the PDF I was able to modify VW values, but still can't figure out the translation from VM to Modbus register address.

If I set the Float/Integer to VM.60, what is the modbus address register that needs to be changed in order to send a float to the logo ?

Thanks,

Luís

Modbus register address:  

40000 + (60 / 2) + 1 = 40031

Please avoid using a "float". A floating point number is 32-bits in size which means it covers 2 Modbus addresses and 4 VB segments. The LOGO does not like working with floating point numbers. Best to keep with INT numbers.

BR