DF1 to Modbus address conversion

[Ozpeter]

I have an existing Micrologix 1400(B) which is being addressed from an HMI via a PCCC/DF1 driver.

However in moving to a new HMI I want to use a Modbus/TCP driver but I don't know how to convert the DF1 style addresses to Modbus style addresses. The following shows the all the different types of DF1 addresses that are used in the existing HMI. Can anyone translate them for me and/or show me where I can learn to translate them myself.

PCCC/DF1             Modbus/TCP
-----------          -----------------
B10:0/10     =>        ??
C5:11.ACC    =>        ??
F21:0        =>        ??
N101:0       =>        ??

 

[bernie_carlton]

There is no direct conversion. Sorry.

For the Micrologix 1400 to act as a Modbus server sepaarate data tables are set up to ACT as Inputs, Coils, Input Registers and Holding Registers.

The PLC program will have to be modified to set up these areas and to move data to these areas and from these areas.

 

[Ozpeter]

Thanks for that. When I had been reading about the Micrologix modbus setup I had a bit of a mental disconnect regarding why the need to specify the range of Modbus addresses. Your reply brings that into sharp focus for me.

Now I have to decide whether its better to modify the PLC program or go with a PCCC driver for the HMI. I'm guessing that the driver may make things easier all around.

 

[Ozpeter]

Well now I am not 100% sure.

Buried in the Micrologix instruction set manual (1766-rm001) on page 561 (well 585 of the PDF) is the Modbus to MicroLogix Memory Map - Summary table which seems to show the relationship between Modbus Addressing and the MicroLogix Addressing Files

Can you comment on that table?

 

[Firejo]

As I understand it:
When you set the channel 0 port up as a Modbus Slave port, you then need to setup the “Modbus Data Table File Numbers” section in the channel configuration. This creates an association between Modbus commands and files in the “Data Files” tree (for example, “Coils” would be “N10:0”). This way when you do a Modbus read of “10001” then you would be reading the status of “N10:0.0”. The table you are refereeing to simply shows you the different file types that can be used for the different types of Modbus commands.

 

[Ozpeter]

I'm learning as I go!

But I think that I have found the definitive issue for what I am trying to do. Page 424 of that same manual shows the configuration of the Modbus Data Table File numbers for each of the Modbus commands … 0xxx, 1xxx, 3xxx and 4xxx. The critical statement on the top of the next page is:

The parameters File Numbers for Coils, Contacts, Input Registers and Holding Registers are configurable, with B or N files only. Valid range is 0, 3, 7, 9...255.

Some of my targets are F and C files. So it seems that Modbus address precludes me from directly accessing those values. So it's back to either modify the PLC program to shuffle things about (well actually my clients program that he has deployed in multiple, different locations) or go to an Ethernet/IP driver and use native micrologix addressing.

 

[bernie_carlton]

I'm betting option #2 will be much less of a headache.