|
<< Click to Display Table of Contents >>
Function Codes |
A function code identifies a message's purpose. There are two groups of functions, one for requests and another one for answers. There are several types of functions for requests, as shown on the next table. Functions for answers are used internally and they are not available to users.
Function Codes
Code |
Function |
Description |
|---|---|---|
1 |
Read |
Requests the specified objects from the remote station. Responds with the requested objects that are available |
2 |
Write |
Stores the specified objects on the remote station. Responds with the operation status |
3 |
Select |
Selects or triggers output points but does not configure or produce any output, such as controls, setpoints, or analog outputs. Responds with the operation status. The Operate function must be used to activate these outputs |
4 |
Operate |
Configures or produces actions on outputs or previously selected points using the Select function |
5 |
Direct Operate |
Selects and operates the specified outputs. Responds with the control points' statuses |
6 |
Direct Operate NO ACK |
Selects and operates the specified outputs and does not send a response, but it takes less time |
7 |
Immediate Freeze |
Copies the specified objects to a freezing buffer |
9 |
Freeze and Clear |
Copies the specified objects to a freezing buffer, then zeroes these objects |
10 |
Freeze and Clear No ACK |
Copies the specified objects to a freezing buffer and then zeroes these objects, but does not send a confirmation response |
11 |
Freeze with Time |
Copies the selected objects to a freezing buffer at the specified moment, responding with the operation status |
13 |
Cold Restart |
Performs a reset sequence |
14 |
Warm Restart |
Performs a partial reset sequence |
20 |
Enable Unsolicited Messages |
Enables a spontaneous notification for the specified objects |
21 |
Disable Unsolicited Messages |
Disables a spontaneous notification for the specified objects |
22 |
Assign Classes |
Links the specified objects to a class |
23 |
Delay Measurement |
Allows an application to calculate a delay or propagation time for a specific station |
Afterspecifying a message's purpose (APCI), there is a second part, if needed, called ASDU. Each ASDU is formed by one or more data identifiers (DUI), object headers, and object information or data fields.