Allen Bradley PLC Data Address Format

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Introduction

There are two distinct ranges of Allen Bradley PLCs:

Model TypesSummary
SLC-500,
MicroLogix,
PLC-5.
These models are configured using ladder logic and store data in files. Tags in Fernhill SCADA are mapped to locations in the data files. The File Data Address Format defines which location in the PLC is mapped to a Fernhill SCADA Tag. Fernhill SCADA uses this tag format when the PLCType Configuration Property is set to 0 (Micrologix, SLC and PLC-5).
ControlLogix,
CompactLogix.
These models implement the IEC-61131-3 standard and each data item is assigned a unique variable name. Tags in Fernhill SCADA are mapped to variables in the PLC program. The Variable Reference Format defines which variable in the PLC is mapped to a Fernhill SCADA Tag. Fernhill SCADA uses this tag format when the PLCType Configuration Property is set to 1 (ControlLogix or CompactLogix).

File Data Address Format

This File Data Address Format is used with MicroLogix, SLC and PLC-5 range of PLCs.

The File Data Address Format is a string that defines the location of data in a file based Allen Bradley PLC. The format of the string is:

Xf:e.w/b

Where:

File Type

Data in Allen Bradley PLCs is stored in files. For example there are separate files for Inputs, Outputs, Status Bits, Timers, Counter, Integers and so on. Some file types are fixed, for example there can only be one file each for Inputs, Outputs and Status Bits. Other files are more flexible, for example there can be multiple Integer files.

File TypeNotes
O Outputs If used, the File Number must be 0.
The Element Number sets the I/O slot.
The Word Offset sets the word offset within the I/O slot.
The Bit Offset sets the bit number (0-15).
I Inputs If used, the File Number must be 1.
The Element Number sets the I/O slot.
The Word Offset sets the word offset within the I/O slot.
The Bit Offset sets the bit number (0-15).
S Status If used, the File Number must be 2.
The Element Number sets the status word.
The Bit Offset sets the bit number (0-15).
B Bit The File Number sets which bit file to use (3, 9-255).
If not used, the File Number is 3.
The Element Number sets the word.
The Bit Offset sets the bit number (0-15).
T Timer The File Number sets which timer file to use (4, 9-255).
If not used, the File Number is 4.
The Element Number sets the timer index.
The Word Offset sets the word offset within the timer (0-2).
The Bit Offset sets the bit number (0-15).
C Counter The File Number sets which counter file to use (5, 9-255).
If not used, the File Number is 5.
The Element Number sets the counter index.
The Word Offset sets the word offset within the counter (0-2).
The Bit Offset sets the bit number (0-15).
R Control The File Number sets which control file to use (6, 9-255).
If not used, the File Number is 6.
The Element Number sets the control index.
The Word Offset sets the word offset within the control (0-2).
The Bit Offset sets the bit number (0-15).
I Integer The File Number sets which integer file to use (7, 9-255).
If not used, the File Number is 7.
The Element Number sets the word.
The Bit Offset sets the bit number (0-15).
F Float The File Number sets which float file to use (8-255).
If not used, the File Number is 8.
The Element Number sets the float index.
ST String The File Number sets the which string file to use (9-255).
The Element Number sets the string index.
The Word Offset sets the word offset within the string (0-41).

File Number

In an Allen Bradley PLC data is organized into files. The File Number is optional and, if included, sets which file to access. If the File Number is not included the file number is implied by the File Type. All PLCs have a predefined set of files as follows:

FileType
0Outputs
1Inputs
2Status
3Bit
4Timer
5Counter
6Control
7Integer

Notes:

  1. On a MicroLogix 1000 PLC no additional files can be defined.
  2. On a MicroLogix 1200 PLC, SLC 5/01 CPU, or SLC 5/02 CPU file 8 is reserved. Additional file numbers 9 to 255 are user defined.
  3. On a other PLC types file 8 is a Float file. Additional file numbers 9 to 255 are user defined.

Element Number

The Element Number sets which element of the file to access.

For Input and Output files, the Element Number indicates which I/O slot to access. An I/O slot may consist of 1 word, or multiple words depending on the type of I/O configured.

For other file types, the Element Number sets which element to access.

Word Offset

The Word Offset field is optional, and if used, defines which word of a multi-word element to access.

Bit Offset

The Bit Offset field is optional, and if used, defines which bit of the word to access.

Data Address Editor

The Data Address Editor provides a convenient tool to build Allen Bradley File Data Address strings.

To open the File Data Address Editor, click on the Browse button Browse button at the right side of the DataAddress field:

Allen Bradley Data Address Editor

Variable Reference Format

The Variable Reference Format is used with CompactLogix and ControlLogix PLCs.

The Variable Reference Format is a string that defines the location of variable in a tag based Allen Bradley PLC. The format of the string is:

Variable[VarArrayIndexes].StructMember[ArrayIndex]

Where:

Examples

Some examples of Allen Bradley File Data Addresses:

AddressDescription
O:1, O0:1, O:1.0The first word of output slot 1.
O:1/0, O0:1/0, O:1.0/0The first bit of the first word of output slot 1.
I:5.1, I1:5.1The second word of input slot 5
N:20, N7:20Word 20 of the default integer file
N:20/15, N7:20/15Bit 15 of word 20 of the default integer file
N10:15Word 15 of user defined integer file 10

Some examples of Allen Bradley Variable References:

AddressDescription
FlowTemperatureA reference to a variable called FlowTemperature.
SCADAData.PressureA reference to Pressure member of the variable SCADAData.

Where Used

The Allen Bradley PLC Data Address Format is used in these contexts:

Further Information

Allen Bradley Register Block Tag

To learn about Allen Bradley Register Block Tags.

Allen Bradley Driver

For an overview of the Allen Bradley Driver.

Glossary

For the meaning of terms used in Fernhill SCADA.