Process Command Source (PCMDSRC)

The Process Command Source (PCMDSRC) instruction selects the command source for a device.

The instruction includes these command sources:

Available Languages

Ladder Diagram

Function Block Diagram

Structured Text

PCMDSRC (PCMDSRC tag);

Configuration Operands

P_COMMAND_SOURCE Structure

Operation

The instruction uses these command sources. The command sources are prioritized in order from highest to lowest in this table.

The instruction enables or disablesthese operations:

The instruction checks for invalid configurations of control and forces the nearest valid configuration.

The core control model arbitrates the source of the commands and parameters that the receiving function accepts. The core control model determines if the source is:

Locking a command source prevents the other command source from acquiring privilege.

Core command source model

The core control model consists of these command sources:

The control model defaults to this configuration. Other command sources may be present in the model but act as overriding command sources, acting independent of the base Operator/Program state machine.

Enabling command sources as configuration

The individual command sources may be enabled or disabled by the user. The default configuration uses the entire base model; upon power-up of the processing environment the command source will be the designated default. Some combinations of enabled command sources are disallowed as they are either unnecessary or could create unintended changes.

Prog Power Up

Configuration allows the user to specify whether Operator or Program is the power-up default.

Prog Priority

Configuration allows the user to specify whether Operator or Program commands take priority when simultaneously asserted.

Automatic reset of commands

All commands are treated as one-shot-latched. This means that all commands are automatically cleared when the instruction executes and processes them.

Changing Destination States

Under certain configurations the destination command source for some commands may change. This is in keeping with the intent of the command. For example, if the Prog is disabled, the destination of the OCmd_Prog command is directed to the ProgLocked state instead of the Prog state. This maintains the intent of the OCmd_Prog command: the operator entity wishes to place the function in control of the program. If the command was eliminated there would be no way to accomplish this. This is only done in configurations where it would cause no conflict or race condition, but serves to preserve as much user functionality as is practical.

Higher Priority Command Sources

These Higher priority command sources operate independently within the model:

Initialization

The instruction is normally initialized in the instruction first run. Re-initialization can be requested any time by setting Inp_InitializeReq = 1. For proper initialization, when adding the instruction while performing an online edit of the code, make sure that Inp_InitializeReq = 1 (default value).

Monitor the PCMDSRC Instruction

Use the operator faceplate from the PlantPAx library of Process objects for monitoring.

Affects Math Status Flags

No.

Major/Minor Faults

None specific to this instruction. See Index Through Arrays for array-indexing faults.

Execution

Ladder Diagram

Function Block Diagram

Structured Text

In Structured Text, EnableIn is always true during normal scan. Therefore, if the instruction is in the control path activated by the logic it will execute.