Bradley Smoker PLC-5 13-14Programming Considerations, I012, Program can be, Interrupted

13-14Programming Considerations

I:012

01

I:012

01

I:012

03

I:012

04

Influencing Priority Scheduling

Use the UID (user interrupt disable) and UIE (user interrupt enable) instructions to influence user program scheduling. They can be used to protect important portions of ladder logic that must be executed through to completion. The UID/UIE instructions are designed to be used in pairs. For example:

I:012	I:012	O:013	Program can be
		02	interrupted
02	03
		UID
I:012		O:013
		02	Program cannot be
04
			interrupted

I:012		O:013
	02	03	Program can be
		UIE
			interrupted

After a UID instruction has executed, interrupts are postponed. The interrupt program is placed in the ready state. After a UIE instruction has executed, any user programs that are currently in the ready state are checked for priority. If the ready program is of a higher priority than the currently executing program, the executing program returns to the ready status while the interrupt program begins executing. While the controller is executing within a UID/UIE zone, the executing program cannot be interrupted except by a fault routine.

For more information on programming UID or UIE instructions, see the PLC-5 Programming Software Instruction Set Reference, publication 1785-6.1.

Publication 1785-UM012D-EN-P - July 2005