interface RS-232 / Jbus protocol

[jsrinivasu]

I new to modbus protocol. I like to interface the CGA Unit (Oldham Make, for using in mining industry, the CGA Unit is connected to 16 underground sensors, it has one monitor to display the status of the sensors) with a host computer.

The CGA Unit uses modbus protocol for interfacing. it has a RS232 port opened for programming.

Can anyone suggest me ,how to interface? I tried with Modbusview, mbslave, mbmaster, calpoll softwares but i have not got any reply from the Unit.

How to proceed further.

Can anyone help me.

Thanks for your kind

J.srinivasu

 

[Macbeth]

Unit should be setup as slave.
Modbus has two formats ASCII and RTU make sure Host and Unit are the same.
Make sure host and unit are different addresses.
Verify both have Same Number data Bits, Baud, Stop bits & Parity.
Verify Cabling try Xing pins 2&3.
Most problems involve cabling.

For cabling Try this:
On the host side:
Jumper Pins 1-4-6
Jumper Pins 7-8

On the slave side:
Jumper Pins 4-6
Jumper Pins 7-8

Interconnect:
2-3
3-2
5-5

What kind of pin out do you have on your unit DB9F?
What are you using to communicate with Computer with what driver?

 

[jsrinivasu]

Dear Mr.Macbeth

Thank you very much for your suggestions. The equipment was manufactured by oldham, france. They used JBUS Protocol not modbus.

We are trying to get the data from normal rs232 cable without any interconnect. The instrument has one serial port opened for programming. we don't know the jumper settings of the instrument. because, the owner of the equipment not allowed to do so.

I am very new to rs232. so give me in detail how to make the cable. I am sorry to say that i do not understand how to make the jumper settings on client side.

we are not using any drivers to communicate with equipment. Is it neceesary to have the drivers to communicate?

Thank you very much for your help.

regards

 

[Macbeth]

J-Bus is a French clone of Modbus. There is only one small difference: registers are counted from 0 (instead of 1) up to hex FFFF instead of (dec) 9999.
Some Modbus masters not all subtract the 1 automatically before sending a message and some slaves add 1 to get at the requested register. So you could end up with accessing a register off by one, but that's the only difference that I am aware of.

OK you probably already knew that. When you say interface I assume you are trying to get the information into a computer via rs232 and then display in some sort of software package. If you could define more of what you are trying.
For cabling RS232 has to types of ports DTE (Data Term Equipment) and DCE (Data Communication Equipment) the only difference is pins 2 and 3 (Rx & Tx) are reverse. When two port types are the same you need what is called a Null Modem adapter or just X connect pins 2 and 3.

Computer (DTE) Unit (DCE)
2----------------------------------2
3----------------------------------3

5----------------------------------5

1----|
4----| |------4
6----| |------6

7----| |------7
8----| |------8



Computer (DTE) Unit (DTE)
2----------------------------------3
3----------------------------------2

5----------------------------------5

1----|
4----| |------4
6----| |------6

7----| |------7
8----| |------8

 

[jsrinivasu]

Dear Mr.Macbeth

Thank you very much for your kind information. I will get back to you after my testing.

Thanks and best regards

jsrinivasu

 

[fernandoelec]

jsrinivasu,

In addition to Macbeth info, you must to have the Mapping register of the device, cause when you´ll obtain communication you have to test the info. If you don´t know how to do the cable, let me to know, to give you some addresses where explain step by step the Job.

If you can´t communicate with the softwares describes by you before, I recomend to you write your own driver, if you need the algorithm i can give you too.

Good Luck,

Fernando Sanchez

 

[fernandoelec]

jsrinivasu,

In this address you can find all that your need about of Modbus protocol:

http://www.modicon.com/techpubs/toc7.html

Fernandop Sánchez

 

[jsrinivasu]

Mr.Fernandoelec

Thank you very much for your information. I know that the register address is 155(hex). I don't know the entire register.

Please give the details of cable.

The all above softwares are not communicating with the instrument. Also let me know the algorithm for writing my own driver for it.

Thanks in advance

jsrinivasu

 

[Macbeth]

The RS232 cable is not some thing unique to Jbus, The cable lay outs above should get you working.. Try the cables without the jumpers. But you can find much info on rs232 at sites like bellow.

http://www2.rad.com/networks/1995/rs232/common.htm#common

As far as drivers go I have found that OMNI Server is a good for things such as this it comes with a modbus prototype configuration that works great for reading registers. You would be able to setup excel to read your point via DDE and then open the included I/O monitor and watch the status and data flow at the comport. This is nice incase the device is giving an error. You will be able to see it. Download this demo it will run for an hour but it may help.

http://www.softwaretoolbox.com/store/item_pages/itempage_950.asp

 

[fernandoelec]

jsrinivasu,

In the following address you can to find all the information about the Modbus protocol:

http://www.modbus.org/default.htm

In the section Modbus serial line, in the category column, you must to choose "implementation guide", there you'll find a file calling "Modbus_over_serial_line_V1.pdf". Then downloading it and you´ll find the algorithm, cable, examples,etc...

I hope that you can solve your problem, if you need another information please let me to know. Other important thing is that you have complete the MAP register of your device to make the test and programming.

Good Luck and Happy New Year.

Fernando Sánchez