Rox
Hi, I'm trying to configure one Modbus slave and I'm getting the message " Please fill out all the fields before saving", my slave only supports 16 Coils and one holding register. what's Im missing?

Thanks, Rox

slave config.jpg 
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thiagoralves
You must fill out all fields to save. If you're not using a particular register, just put 0 on the start address and 0 on the size. From your picture I can see that holding registers (write) start address and discrete inputs start address are not filled.

Also, your start address for holding registers (read) and coils is wrong. The "start address" field is related to the modbus device, not OpenPLC. You don't put OpenPLC locations in there. If you want to read all registers of the device, you need to start at register 0 (then start address is 0) and then on "size" you put the amount of registers the device has. The start address allows you to instead read just half of the registers, or a segment of registers in the device.
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Rox
Got it! Thank you.
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Rox
I continued working on my RPI, still have problem, the RPI are now able to read my MB slave registers, i have pots on my slave that is displaying correctly on Web server Monitoring as shown below addressed %IW100 and %IW101, but can't read from modbus master simulator, it's always zero with modbus holding reg addresses 1024 and 1025. can anyone point where im doing wrong.
Thanks.

openplc2.jpg    
openplc1.jpg 
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Rox
Solved! i had to copy/move the input register into holding register!! %MW0 = %IW100.
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thiagoralves
Instead of moving the values you could also use Input Register on Radzio instead of Holding Register. Input Register is for %IW inputs. Holding register is for %QW, %MW, %MD and %ML variables.
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