Bradley Smoker PLC-5 user manual Program Execution States, 13-12Programming Considerations

13-12Programming Considerations

This scheduling determines what controls the program execution path. For example, if a PII is currently executing, it cannot be interrupted by an STI until the PII is completed (since the PII has scheduling priority over the STI). If an MCP is executing and a fault routine is called, however, the MCP’s execution will be interrupted because fault routines have priority over the MCPs.

IMPORTANT

You can temporarily override this priority scheduling by using the UID and UIE instructions. These instructions can be interrupted by a fault routine (see page 13-14).

Fault routines, PIIs, and STIs are interrupt driven. They can execute at any time except during run-time edit operations. MCPs, however, are executed to completion from first user program to last.

Program Execution States

User programs in the PLC-5 controller are always in one of the following five states: completed, ready, executing, waiting, or faulted.

Publication 1785-UM012D-EN-P - July 2005