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Old March 16th, 2014, 04:14 AM   #1
ansariobaid
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Question GE Versamax Modbus Comm.

Hi Everyone!!!
I want to establish a Modbus communication between Versamax PLC CPU001 (Master) and RX3i PLC CPU CPE305 (slave) on Port1 (RS232). I have tried Sample application program provided in GFK2220E manual but to no avail. Can any one please help me out???
Is there any program code available for the same???


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Old March 16th, 2014, 01:29 PM   #2
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There are several common mistakes. First, make sure all of your COMMREQ instructions are triggered by one-shots. Make sure the %R addresses you use for the COMMREQs aren't being written to anywhere else in your program. Make sure you have selected the correct SYSID and TASK for the COMMREQ instruction. Make sure you have entered all data properly in the BLK_MOV instructions that set up the COMMREQs. Pay particular attention to hex vs decimal data.

What code do you get in the COMMREQ status word?
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Old March 16th, 2014, 04:30 PM   #3
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And triple check your serial cable.
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Old March 17th, 2014, 03:56 AM   #4
ansariobaid
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GE Versamax Modbus Comm.

Dear sir,
I am new to GE and Modbus both, so am not quite acquainted with the systematic approach for establishing Modbus communication. How should I proceed to accomplish the communication? Please find the attached program file which I have written for the Modbus Master Communication. And the master to slave serial cable is same as that of the RX3i RS232 programming cable, will it do?


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File Type: zip VMax Modbus Comm.zip (25.6 KB, 170 views)
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Old March 17th, 2014, 10:15 AM   #5
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Look at the configuration of that CPU, the serial ports on it can be configured for "Slave" only when used as "RTU Only" That is true of Port 1 and 2.
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File Type: png RTU.png (23.7 KB, 236 views)
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Old March 17th, 2014, 10:56 AM   #6
ansariobaid
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GE Versamax Modbus Comm.

Dear Sir,
As far as I know the modular VersaMax CPUs are configured as RTU slave in hardware configuration, but can be reconfigured as master via ladder logic.


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Old March 17th, 2014, 12:17 PM   #7
RussB
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Quote:
Originally Posted by ansariobaid View Post
Dear Sir,
As far as I know the modular VersaMax CPUs are configured as RTU slave in hardware configuration, but can be reconfigured as master via ladder logic.


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You are correct, very sorry, I had forgotten that, been a while for this serial stuff.
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Old March 17th, 2014, 01:32 PM   #8
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It may work better, if you set Port 1, as it is what you say you are using.
This is one of the Rung Comments in the RTUINIT Block.
"This block initializes Port 2 for Modbus RTU master operation."

Sorry if your documentation is incorrect but you did not ask that be checked too. Only time for one step at a time here.
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Old March 18th, 2014, 05:07 AM   #9
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Dear Sir,
Thanks for the reply and Sorry for the documentation mistake. As I said am not quite acquainted with the procedure to set up the Modbus Communication and this is the first time I am doing the communication part.I just gone through the sample program provided in the GFK2220E Manual. I've been trying the same since last three days, but could not accomplish it. If convenient, request you to please provide me the systematic procedure required to set up the communication successfully.

I'll be grateful for your assistance.

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Old March 18th, 2014, 10:46 AM   #10
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Another observation, that I am assuming because of lack of facts.
You say that: "And the master to slave serial cable is same as that of the RX3i RS232 programming cable, will it do?"

If you have an IC693CBL316 I don't believe it will work, look at the pin configuration of each port and the cable pin configuration. This cable will attach the TX of the RX3i to the TX of Port 1 on the VersaMax and the RX to RX.
Please build a proper cable based on the two pin configurations, also I would recommend a jumper on RTS to CTS at each end. These are in the manuals or you can find them in links here: http://forums.ge-ip.com/showthread.p...0395#post60395
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Last edited by RussB; March 18th, 2014 at 10:52 AM. Reason: SP
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Old March 19th, 2014, 04:55 AM   #11
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Dear Sir,

Thank you very much for your kind response. I have prepared the Serial Cable according to below mentioned pin configuration.

Versamax PLC RS232-----------RX3i PLC RS232
(DB9 M)--------------------------(RJ25)

02(TXD)--------------------------05(RXD)
03(RXD)--------------------------02(TXD)
05(GND)--------------------------03 & 04 (GND)
07(CTS)----08(RTS)&-----&-----& 01(CTS)----06(RTS)

Now, I want to make a program to check the Modbus communication, I am using the same program logic that is provided in the GFK2220E manual but am not getting the result. How should I proceed to accomplish the Modbus communication? or How can we check that the communication is done or not? Awaiting your kind response.

Last edited by ansariobaid; March 19th, 2014 at 05:02 AM.
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Old March 19th, 2014, 10:37 AM   #12
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Triple check that you have no programming errors from copying the example logic from the GFK-2220 manual (Sure wish GEIP supplied these examples.) and triple check that any adjustments made to this logic to fit your system are correct.
When time to run the logic make sure that the COMM REQs are enabled in the proper order.

First the the CR to change port 1 to "Master" making sure that the "Status Register" has a value of "1" anything else is an error and your port is not setup properly.

Now begin the CRs to "read and write" Making sure that ONLY 1 CR to this port is called at any point in time and that its SR has a value of "1" before any other is enabled.
If the SR is >1 look up the error in the GFK-2220 manual and fix it.

I find it helpful to move the SR into a holding Register or two so I can see the last couple of errors.

See also: http://forums.ge-ip.com/showthread.php?t=9219
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Last edited by RussB; March 19th, 2014 at 10:44 AM.
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Old March 20th, 2014, 09:54 AM   #13
ansariobaid
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Versamax Modbus Master Slave Comm.

Dear Sir,

I have configured the CPU RS232 Port (port1) as a Master and the value in the status COMMREQ word is 01. Now When I am trying to make a READ request it is showing fault and the value in status reg is 1795. Please find the attached program for your review. The REED block is for READ request, STAT block is for reading Diagnostic status word and RD block to monitor the register values. Please assist me to figure it out.

I'll be grateful for your assistance.

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File Type: zip ModbusComm.zip (28.5 KB, 105 views)
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Old March 20th, 2014, 10:59 AM   #14
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I do not have time to dig into your program now, maybe someone else will but I did find this on the GEIP Support Web site maybe it will help.

What manual GFK-2220D page 33 says about your Fault 1795 if this is Hex 0703, is that this is a Parameter Error - "The RTU Function Code is not supported." This is word 9 of your command block the Read function Code should be from the Table on page 31.
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File Type: zip Serial_COMMREQ_Example.zip (61.8 KB, 179 views)
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