Configuring Variable Tags
- Last UpdatedAug 04, 2025
- 2 minute read
Variable tags are addressed using the alias names defined in OPC Factory Server (OFS). The following table demonstrates the variable tag address formats you can use to read values.
When specifying a data type, consider whether the server will be able to convert data to the requested type.
|
Address |
Plant SCADA type |
OFS Type |
Example |
|---|---|---|---|
|
[<alias>!]<item_id> |
digital |
vt_bool |
bool_symbol or |
|
[<alias>!]<item_id> |
byte |
vt_ui1 |
byte_symbol or |
|
[<alias>!]<item_id> |
int |
vt_i2 |
int_symbol or |
|
[<alias>!]<item_id> |
long |
vt_i4 |
long_symbol or |
|
[<alias>!]<item_id> |
real |
vt_r4 |
real_symbol or |
|
[<alias>!]<item_id> |
string |
VT_ARRAY of |
string_symbol or |
Plant SCADA also allows a collection of variables to be associated with an OFS array tag. The following table demonstrates the variable tag address formats used to read values from OFS array tags.
See also Array Support.
|
Address |
Plant SCADA type |
OFS Type |
Example |
|---|---|---|---|
|
[<alias>!]<item_id>!a[size] |
digital |
array of |
dig_array!a[32] or |
|
[<alias>!]<item_id>!a[size] |
byte |
array of vt_ui1 |
byte_array!a[10] or |
|
[<alias>!]<item_id>!a[size] |
int |
array of vt_i2 |
int_array!a[10] or |
|
[<alias>!]<item_id>!a[size] |
long |
array of vt_i4 |
long_array!a[10] or |
|
[<alias>!]<item_id>!a[size] |
real |
array of vt_r4 |
real_array!a[10] or |
Tag addressing for bits
The following table defines the syntax for configuring the tag that represents the bit of a WORD or INT UnityPro data type.
|
Address |
Plant SCADA type |
UnityPro Type |
Example |
|---|---|---|---|
|
[<alias>!]<item_ID>.<bit number> |
digital |
INT or WORD |
MyInt.0 Or PLC!MyInt.1 |
The item_id above can be either a symbolic or direct address.
The direct address syntax is shown below:
-
Single variable: [<alias>!]<direct_address>
For example: PLC1!%MW1
-
Array of variables: [<alias>!]<direct_address>:<size>!A[<size>]
For example: PLC1!%MW1:10!A[10]
Note: The driver will poll some of the OFS special items instead of subscribing to the item value updates. For more information, refer to Poll Engine for #Specific Tags.