Read Tags
- Last UpdatedAug 04, 2025
- 2 minute read
Read tags can be used to retrieve data from IO points that require a read command. See Using Read Commands to Retrieve Data.
<IOA> is used to represent an information object address, defined as a decimal number in the range 0 — 16777215.
Note: The tags with the following addresses are only updated when the driver receives a
timestamped value directly from a device.
• RSD<IOA>
• RSI<IOA>
• RSL<IOA>
• RSF<IOA>
• RSQD<IOA>
See Timestamp Handling for more information on the correct syntax to use for your input tags.
|
Address format |
Plant SCADA type |
IEC 60870 type |
Description |
|---|---|---|---|
|
RD<IOA> RSD<IOA> |
DIGITAL |
Single point Double point |
Read command for digital value: Example: RD100 Note: By default, digital tags report double point states as: |
|
RI<IOA> RSI<IOA> |
INTEGER |
Measured value: Step Position Double Point |
Read command for integer value: Example: RI200 |
|
RL<IOA> RSL<IOA> |
LONG |
Integrated totals |
Read command for long value: Example: RL300 |
|
RF<IOA> RSF<IOA> |
FLOAT |
Short Floating Point |
Read command for float value: Example: RF350 |
|
RQD<IOA> RSQD<IOA> |
INTEGER |
Quality descriptor |
Read command for IEC 60870 quality flags and the IEC870IP driver specific flags Example: RQD350 |
The address format used in the table above demonstrates unstructured tag addresses (i.e. "<IOA>"). The IEC870IP driver also supports structured tag addresses (e.g. "<IOA1>.<IOA2>.<IOA3>"). For more information, see Structured Tag Addressing.
Note: Care should be taken when configuring read tags in a system because the read process is less efficient than the usual spontaneous update process. Due to the polling mechanism, read tags will consume more system and network resources than other tags. For example, if you have more than 500 read command tags configured, it may impact the tag value update rate on a page as the driver will have to issue a read command for each tag on a page.