How to implement Modbus Ethernet communication in Lookout, if we want to simulate the PC as PLC ?

[theta@vsnl.com]

Problem Description :
Dear Sir,

We are doing a project where we are using Lookout with
Front end Modicon PLC. The communication is by
Ethernet, using Modbus.

Since the installation is at a distant place, we wanted
to use another PC (running Lookout) to simulate the
PLC. For this, we tried to communicate

a: the server Lookout PC running Modbus Ethernet mode of
Modbus object as Master

b: with another PC (for simulating the PLC) running
Modbus Slave

We did not get any communication. (we have given the
details of what we have done, at the end of this email)


We also tried connecting the above 2 PC's as

a: the server Lookout PC running Modbus Serial mode of
Modbus object as Master

b: with another PC (for simulating the PLC) running
Modbus Slave object

Again we did not get any communication.


If instead of PC (b) we connect the Modbus simulator to
PC (a), there is no problem in communicating

Please let us know how to go about establishing the
communication between 2 PC's using Modbus serial,
and Modbus Ethernet. A detailed step by step procedure
would help us a lot.


Thanking you

Warm Regards
Raja Mahbubani



Procedure of our trial with ethernet.

This is what we have done in detail.


On PC A::>

We created an object (Pot) and connected it to
the modbus data member of the modbus object say 40001. In the
properties of the modbus object we selected modbus ethernet mode
of communication and in the IP address field we wrote the IP
address of the machine B to which we are trying to communicate
i.e. 152.63.50.2.

On PC B::> we tried the following two methods

Trial 1 : We created a modbus slave object and
inserted an expression for the same data memeber to which the
object was connected hoping to get the value of the pot of machine
A on machine B.


Trial 2 : We created a modbus object on machine B and we wrote
the IP address of machine A and inserted an expression for the
same datamemeber to which the object was connected hoping to get
the value of the pot of machine A on machine B.


NI Software : Lookout
Version : 4.0.1 or 4.5
OS : Windows 98
NI Hardware : N/A
Drivers : N/A
Other Hardware/Instruments : N/A
CPU : Pentium
RAM : 64
Vendor : S-Tech

Customer Information :

Raja Mahbubani
Theta Controls
IN
theta@vsnl.com
Ph: (+91) 20 4222556/7

[Khalid]

.


The ModbusSlave which comes with Lookout currently supports only Serial communication. So, you cannot use Ethernet between your two PCs. At least not with Modbus Master-Slave setup (if you must speak Ethernet between the two PCs, IPASCII object lets you do that, but then you'll need to implement your own protocol).

Since all you want to do is simulate a Modbus PLC on a PC, you can use the Serial mode of communication for now. And later on just modify the Object in your Server Lookout to use the Ethernet mode.

For setting up a Serial Modbus Slave, use a null-modem cable between the two PCs (lines 2 and 3 are swapped). On your PC 'B,' create the Modbus Slave object with the right COM port for that PC. And on your PC 'A' create the regular Modbus Object as if you w
ere connecting to the Modbus Simulator box. The only difference here is the cable. The simulator box uses a straight-through cable whereas the Slave needs a null-modem cable.

Hope this helps.

Rgds,

Khalid 🙂



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