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25GFK–0644 Chapter 4 Programming Guide
Calling the Program Block
To call the LINKxxX block, place a Call instruction as close as possible to the start of the
main program. To assure consistent mapping of link I/O data, do not use permissive
logic to the call. Include at least one call to the LINKxxX block each program sweep, to
assure that the link status is routinely updated and the link retry mechanism is enabled.
This is discussed in more detail later in the chapter.
Example Call Instruction
In this example, the Call instruction calls Program Block LINK73X.
[ INTERRUPTS ]
[ START OF PROGRAM BLOCK ]
CALL LINK73X
Using Multiple Calls to the Program Block
For most applications, the main program will include only one Call instruction to the
LINKxxX Program Block. However, it is possible to use multiple calls in the program. For
example, a call might be used at a particular place in the program to update inputs, outputs,
or both. In this way, the Program Block call would serve as a “Do I/O” instruction.
In applications with long communications windows or in Constant Sweep Time mode, a
call to LINKxxX might be used at the beginning of the program to update only inputs,
with another call at the end to update only outputs.
When using multiple calls to the LINKxxX Program Block, all additional calls after the first
should use the set status of the “Link Active” status bit as a permissive to their execution.