LabVIEW Modbus TPC

[meihk]

HI.

I'm working on a LabVIEW small project. What I do now is trying to config LabVIEW as a Modbus TCP Master. However I have not received the Modbus slave yet, so I try to use a simulator software instead.

I config my PC's IP: 192.168.2.3 (same as address string in the "Creat TCP Master VI" block).

Port is 502.

Write starting address is 0

Write values are temperature and pressure

Read starting address is 5 (for example)

Read count is 1

Read values to a variable named "control signal"

I used the modbus simulator soft below

But the problem is: the values write from LabVIEW (temperature and pressure) are written to address 40001 and 40002. But the "control signal" is taken from 40006. I thought it has to be 30006. Right?

I tried another simulator soft (the last pic) but both write and read didn't work.

(Sometime it's error 538181, sometime error 56)

Could you suggest me the solution?

Thank you.

[RavensFan]

A register beginning with a 3 is an input register.   You can only read from the slave.  You use modbus command code 4 "Read Input Register to get the value".

A register beginning with a 4 is a holding register.  You can read or write to the slave.  You use modbus command code 3 to "Read Holding Register", command code 6 to "Write Single Register", or 16 to "Write Multiple Registers".

Note that the 3 or 4 that is part of the register address is never transmitted.  And that the registers beginning 3 or 4 always start at 1,  while the protocol messages start at 0.

So 30006 is read using Read Input Register, and the value is 5.

Since you are using a subVI that is Write and Read Multiple Registers, it must be a Holding Register and is thus 40006.

You need to use Read Input registers with a 5, to read register 30005.  You can't write to it.  You need to do something on the slave side or the slave simulator to enter a value there.

[meihk]

Oh right. I see it. Thank you so much for your specification.