Modbus Master from Rockwell

plcnovel · Apr 13, 2006

Hello Everybody
I have attached a demo version of the Modbus Master for Logic controllers from Rockwell (zip file contains both master and slave....i am reffering to Master).I haven't gone through this program,and before i go through this program, i would just like to pass it on to every body on the forum to take a look at it. Point is to clear following things:
Did anybody use it before? if yes, what is the success rate of this program? Also if you guys share your thoughts after going through the ladder logic, it will be a great help for me when i get a chance to go through it. Thanks in advance

Regards

Contr_Conn · Apr 13, 2006

Did you try it?
Why you asking us to try it?

These programs included in standatd installation of RSlogix5000 since ver 13
I used them and they working. Just dont expect any performance from the PLC serial port - it has lowest priority. If you need fast application, use prosoft module.

plcnovel · Apr 13, 2006

Hi Contr-Conn

I haven't try them yet....that was the reason i asked if someone out there tried it, hows the performance and views....Thats what i wanted to collect from this thread. Anyway thats good taht you have tried them. In my case i just want to read the data from the slave. My slave doesn't allow me to write anything. basically i want use Modbus function codes (01, 02, 03 and 04). My question is do i have to still use the complete code in order to make it wroking or i can cut down the code. Since i am not that experience with plc programming, if i can cut down some code what should i take out in order to implement the above function code. Thanks

Contr_Conn · Apr 13, 2006

You probably strip some code down, but at this point you will be on your own. You will not see any performance difference.

plcnovel · Apr 13, 2006

Hi To Everyone

My slave is on RS-485, and i am using Compact logic processor (L35E)'s serial port. How can i connect these two devices physically so that i can use that ModbusMaster.ACD demo. Like do i have to use Null modem cable for it? or something else

thanks

Contr_Conn · Apr 13, 2006

Use NET-AIC module or any other RS485-RS232 converter.

Also keep in mind that application supports Modbus Register and Bit addresses lower than 32767 only (7FFF HEX)
To address full range up to FFFF some code modifications required.

plcnovel · Apr 17, 2006

Contr_Conn said:
Also keep in mind that application supports Modbus Register and Bit addresses lower than 32767 only (7FFF HEX)
To address full range up to FFFF some code modifications required.

I need to read function code 01, 02, 03, 04, would this application do this or do i have to modify the code?

Contr_Conn · Apr 17, 2006

No, you dont need to modify code if your Modbus register/coil address is less than 7FFF hex (32767 DEC)

plcnovel · Apr 17, 2006

Contr_Conn said:
No, you dont need to modify code if your Modbus register/coil address is less than 7FFF hex (32767 DEC)

Lets say i want to read modbus register 40033 or 40034(func code 03), do i have to modify the code for this?

Contr_Conn · Apr 17, 2006

No, these are actually 0033 and 0034
First "4" is for register identification

plcnovel · Apr 17, 2006

Contr_Conn said:
No, these are actually 0033 and 0034
First "4" is for register identification

Is it possible if i want to read specific register value instead of reading the whole range. Whats happening in the code, it is ready the whole range (NumberofPoints). For example lets say i want to read register 30027 to 30033, and then want to read register values 30064 to 30079. Can i do that in the application?

Thanks

Contr_Conn · Apr 17, 2006

plcnovel:

Did you look at this application or you want someone else to do your home work?
Load application, read the manual and find out if it will work for you.
The short answer to your last question: YES.
Try this application and you will definately find your answer.

You don't have to have a Modbus device, tons of simulators availabe for free download.

plcnovel · Apr 17, 2006

Hi Contr_Conn vbmenu_register("postmenu_152977", true);

I am right now working on this projet(online), The maximum number of points i can read in function code 4 is 67, it can't let me read more than 67 points. I want to read more points. Even Out of 67 points , i dont need all of them, but i really dont know how to find a way to read one particular register. I am a little new to this field and learning alongside. Please if you can suggest me something, it will be a great help. Thanks

Contr_Conn · Apr 17, 2006

You can issue multiple commands (up to 40), they will be executed one after another. You can specify ranges separately.

You can't read a single register or coil, you can read range only, but you can write a single register or coil (FN 5 and 6)

plcnovel · Apr 17, 2006

Contr_Conn said:
You can issue multiple commands (up to 40), they will be executed one after another. You can specify ranges separately.

You can't read a single register or coil, you can read range only, but you can write a single register or coil (FN 5 and 6)

Yeah thats what exactly hapening with me. I am using command[0] for function code 4, to read (Numberofpoints = 30, modbus register 40001 to 40030) and starting address for this command is 0 with 0 offset. In Command[1] i am trying to read (func. code = 04, number of points 15, modbus regiters 40063 to 40079). The starting address for this command is 0 with offset=31. But it keeps on reading the first 15 points in this command, never reads register 63 to 79. How can i indicate the range in my command(to read from register 40063 to 40079)? Thanks

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