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Old July 24th, 2016, 10:03 AM   #1
shazad5444
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Modbus Canning Software

Dear Friends, Need your help regarding modbus registers scanning. Right now I'm using Modscan32, but its response is not good. I'm facing following problems with Modscan32.

1. Once you connect your Rs-485 to US connector It shown connected, even you are connected or not with PLC, its very difficult to confirm that whether we have connectivity with PLC or not.

2. In my experience we are mostly getting wrong Modbus registers from manufacturer, so it is very hard to find the correct registers.

Recently I worked with redlion RTU and found it is very user friendly and very simple to scan Modbus registers.

Please advise Do we have any such software where it scan all modbus registers without giving addresses and shows connectivity with PLC.
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Old July 24th, 2016, 10:20 AM   #2
diat150
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I use modbus poll from modbustools.com
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Old July 24th, 2016, 12:30 PM   #3
danw
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1) Modscan32
I have used Modscan32 for some years and it's always been clear to me whether Modscan is connected or not connected.

I do not have resources for an RS-485 serial connection at the moment, but to the best of my knowledge, Modscan uses the same connected/disconnected mode for either, so here's what I see for an Ethernet (Modbus TCP) connection:

When disconnected the "Device not Connected" message shows up in red letters:


When connected, there is no positive message, you just see data for which screen data one is on:


Note that the "Number of Polls: and Valid Slave Responses values increase in real time, at a rate depending on what the polling rate is.

2) >"mostly getting wrong Modbus registers from manufacturer"

That statement is not clear as to whether
a) the manufacturer does not define the Modbus registers in the slave accurately, or
b) the manufacturer does define the data, but the data that you read from any given register is not what you expect.

If your problem is a), poor manufacturer documentation, then changing which Modbus master software you use will not fix anything.

If your problem is b), then the primary reason why you might be getting the wrong data is the dreaded one offset in Modbus register addressing.

Using holding registers, 4xxxxx, as an example,
sometime addressing starts at (4)00000,
other times, addressing starts at (4)00001.

So what the master asks for at (4)00016, might be (4)00015 or (4)00017.

You need to move the addressing up or down by one and see the results are.

If you have a connection and then lose it, that's a different problem altogether.

3) Please provide examples

When you have communications problems, it always helps to provide specific examples (with numbers) of what you expect, and then you actually have, because the comparison can provide valuable information in troubleshooting the cause.

For instance,
I expect 400016 to have the value 465.2, but I got -6.7723^-17

Last edited by danw; July 24th, 2016 at 01:10 PM.
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Old July 24th, 2016, 01:08 PM   #4
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Of the programs I have used, there is generally a need to define the registers you are looking to read /write. If there is one out there that scans all available locations and brings back the 'available' registers- that would be interesting. Maybe dangerous but interesting.

For Modbus TCP I use the Modbus Tester ( though I see it does Modbus serial as well)- from here:
http://www.schneider-electric.com/en/faqs/FA180037/

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Old July 24th, 2016, 04:34 PM   #5
BobB
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I used to use Modscan 32 and now use Modscan 64 - works fine. The best USB/RS485 is this one - FTDI chips I have always found just work for USB to serial. http://au.element14.com/ftdi/usb-rs4...88&CAGPSPN=pla
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Old July 31st, 2016, 09:49 AM   #6
shazad5444
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Dear Friends, Thanks all of you for detailed reply, It looks me the problem is with Hexen RS-485 to RS-232 converter, I tried already 3 converters and same result, Now looking Moxa converter, hope it will work.
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Old July 31st, 2016, 07:13 PM   #7
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I use modbus poll as well. As Diat150 suggested
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Old August 8th, 2016, 12:26 PM   #8
V0N_hydro
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qmodmaster is the best one I have used. it is totally free.
https://sourceforge.net/projects/qmodmaster/
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Old August 9th, 2016, 02:20 AM   #9
shazad5444
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Dear friends bundle of thanks for your great advise and help, finally I found problem in my RS-232 to RS 485 converter. Before I was using Hexin (03 Converters I used) which all were found faulty, bought new MOXA Uport 1150 and got communication. I used Modscan32 and ModbusPoll (MBpoll) and got good response on both of these softwares. Topic is closed and findings are Cheap faulty converter.
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Old August 9th, 2016, 03:10 AM   #10
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Thanks for the update.
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Old August 9th, 2016, 05:45 AM   #11
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Danw also thanks for your great support and gave me brief expatiation.
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