ST_IEC870_5_101GenCmdPollParams

Parameter for cyclic transfer of the data points in control direction (single command, double command, setpoints etc.).

The (high-level) central station function blocks FB_IEC870_5_101Master and FB_IEC870_5_104Master implement a simple/automatic command execution. In its implementation, a command is activated/executed as soon as the process value of a control data point has changed (example: the value of a single command (C_SC_NA_1) changes from OFF to ON). In some cases, however, it may be necessary to resend the values of all control data points to the substation, especially after the loss and restoration of the communication link.

In this case, the cyclic transfer of the data points can be useful. Please note that there may be concurrent access to command execution if, for example, the data points should be cyclically transmitted in the control direction (command execution) and a control data point is already executing a command (by spontaneous value changes at the data point in the control direction). The active command must first be executed to the end. Only then can a new command be activated. Because multiple primitives (activation, confirmation of activation and termination) are involved in command execution, a command execution time of a few milliseconds to seconds/minutes can occur, depending on the system. This should be taken into account when implementing a central station application. Filtering should then be carried out for rapidly changing PLC setpoints. E.g. with analog setpoints, the least significant bits can be masked out. In this way, the number of command activations can be reduced.

In the case of concurrent access to command execution, commands can be activated (repeated) at a later point in time. However, the repeated command is activated with the setpoint available at a later time.

TYPE ST_IEC870_5_101GenCmdPollParams:
STRUCT
    tPollCycle           : TIME := T#1h;
    bEnable              : BOOL := FALSE;
    options              : DWORD := 0;
    bQueueConcurrentCmds : BOOL := FALSE;
END_STRUCT
END_TYPE

tPollCycle: Transfer cycle time.

bEnable: Activates/deactivates the cyclic transfer of the data points.

options: Additional parameters.

bQueueConcurrentCmds: Controls the behavior of command execution if a command is already executed at the time of cyclic command activation (e.g. triggered by a spontaneous value change in the PLC process data):

• FALSE (default value). For data points that are currently executing a command, no repeated commands are activated at a later time.
• TRUE: For data points that are currently executing a command, the command is activated later (after the currently active command execution is complete).