RS485 Limitation

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alamdar.syed
Posts: 4
Joined: 03 Mar 2020, 00:56

RS485 Limitation

Post by alamdar.syed »

Hello
I am working on RS485 chain on Pictory and used 150 Input RTU Master block. This block has 150 Input Words and 32 of each Output Word, Input Bit and Output Bit, therefore total 150+32*3 = 246 inputs and outputs. However, when I was entering the addresses in 'Extended Data' after right clicking the block; it was limited to only 32 total inputs and outputs. I have total 119 Inputs and Outputs, used in my LogiCAD program. Can you please advise some way so that I can use all my I/O?
Thank You
Frank
Posts: 65
Joined: 09 Jan 2017, 10:46

Re: RS485 Limitation

Post by Frank »

Hello Alamdar,

1. please open the 'Extended Data' dialog window by right-clicking on your Modbus Master 150 device
2. in the 'Function Code' column please select 'READ_INPUT_REGISTERS'
3. in the 'Device Value' column you now have a list of all your 150 Input_Word values

Please give me feedback if this advice worked for you ...

Regards,
Frank
alamdar.syed
Posts: 4
Joined: 03 Mar 2020, 00:56

Re: RS485 Limitation

Post by alamdar.syed »

Hello Frank
Thanks for looking into this. The 'Device Value' provide all the I/O available at Modbus block however the column 'Action ID' is limited to only 32 rows. After 32rows when I click 'Add Row', it gives me error as in the below image. How can I use all device values of the block if action ID is limited.
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Error about max row
Error about max row
Max-Rows.PNG (66.22 KiB) Viewed 5340 times
Frank
Posts: 65
Joined: 09 Jan 2017, 10:46

Re: RS485 Limitation

Post by Frank »

Hello Alamdar,

ok, this was a missunderstanding: normally the number of action rows you can add is limited to the number of Action_Status values the device offers.
Under certain circumstances this limitation could be switched off - I'm currently discussing this issue with our Modbus-Expert in the company ...

We will probably offer you a solution for this special case in short-term.

Greetings,
Frank
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dirk
KUNBUS
Posts: 2174
Joined: 15 Dec 2016, 13:19

Re: RS485 Limitation

Post by dirk »

Hi alamdar.syed, there are some adjacent registers. You can combine them with a single action. I.e. rows 14 and 15 may be combined with by reading two registers starting at 53507.
This also applies for rows 30 and 31, etc. This combination of adjacent registers increases the performance of your system. So by doing this combined actions can you estimate that you need more than 32 actions anyway?
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