Modbus RTU with Delta PLC.Need to know configuration setting

Dear sir,
I have been trying to commmunicate ignition scada with Delta PLC (without ethernet) via RS232 and Rs432 seriel communication. But i have been getting error along the tag.


Based on the error shown, it looks like this is a connection issue with the Delta PLC. How do you have this device connected to Ignition?

Dear sir,

Kindly for your information, I have created tags for PLC input Address, PLC output coil, data register and PLC memory bits.

But except PLC memory bits, all the tags i have created functions perfectly and I aslo cross checked the tags by using some logics in my PLC.

In case of PLC memory bits(Address prefix with M and Modbus address starting with 2097) its tag quality toggles continously between Good and Bad.

"How do you have this device connected to Ignition?"
The connection between modbus and the ignition is made via Modbus RTU.


Ajith Arawinth,

Based off of your description, you may get better results by reaching out to our support department so we can troubleshoot further.

Or share some documentation for the PLC you are trying to use.

Dear sir,

The Model of the PLC we have been using is DVP28SV11T2.

For your refernce I have attached the PLC manual.


Ajith Arawinth.M,

(Attachment DVP SV2 MANUAL.pdf is missing)

Firstly, your attachment is not there.

Secondly, please reply on the forum not via email notification, adding your signature to every post is against the forum policy.

DVP SV2 MANUAL.rar (7.8 MB)
Dear sir,
I have been using DVP28SV11T2 Delta PLC and it is communicated to Ignition SCADA via Modbus RTU.

I searched the Delta site myself, since you provided just a programming manual, not a hardware or communications manual. (Though the manual you provided does have the table of Modbus addresses in §2.12.)

I found this document, that describes nearly everything you might possibly want to know about Modbus RTU with these products:

Especially note the contents of the screenshots in §3.2.2.

Did you try checking the box in the server config to enable RS-485?

Dear sir,

Thankyou for your support. I have changed each parameter of configuring the modbus and found that the parameters i have marked in the image attached with this mail may result in the quality change of the modbus tags.


Max Holding Registers Per Request

Maximum number of Holding Registers allowed per read request. 125

(default: 125)

Max Input Registers Per Request

Maximum number of Input Registers allowed per read request. 125

(default: 125)

Max Coils Per Request

Maximum number of Coils allowed per read request. 125

(default: 2,000)

Max Discrete Inputs Per Request

Maximum number of Discrete Inputs allowed per read request. 2000

The numbers in the red colour represent my set value. After set this value all my tags input,output coil,Data register,memory bits all works fine.

But I have an question. May I know what are the functionality of these parameters that i have mentioned in the table. How do they affect the tag quality.


Ajith Arawinth,

The defaults are the maximum allowed by the Modbus protocol. Some devices have problems using the full allowed lengths. (A few even document it.) The values can be reduced to accommodate such devices.

{Please edit your posts to remove the email signature block. You've been asked to not include it, as it violates this forum's rules. If you cannot send email that does not include a signature block, then you should not use the email response option. People who repeatedly violate the rules tend to be ignored by the helpful people here.}

Dear Sir,
I need an clarification.whether changing the value of modus configuration mentioned in the previous discussion will affect any funcionality other than tag quality.
As you mentioned i have edited the email signature block.

I explained why those options exist. A device that needs those options would certainly deliver no values when that problem is encountered, which would show up as bad quality.