Rockwell Automation D64046.5.1 U MNL WIN DDMC - Manual (Page 18)

Chapter 1
Understanding How a DDMC32 System Works
1-6
The instruction scans the inputs from the top of the input list to the bottom,
looking for a transition. When the actual inputs do not match the expected
inputs, the instruction begins scanning the combinatorial equations for a
match and remains in the step until all conditions for the equation(s) are
met. The combinatorial SDS instruction ignores the “expected” entry
states so that, even if possible, no mismatch error is generated.
When a valid transition, a set of conditions as specified by an equation, or
a timeout occurs, the instruction moves to the destination step to verify the
inputs before entering the step (this occurs for transition equations only,
not ANDed conditions). See the following section for information on how
the SDS handles outputs.
How the SDS Instruction Handles Outputs
The SDS instruction sets or resets outputs as it enters each step (based on
how you define outputs in the configuration template). The table below
shows what happens to outputs when the SDS enters an error step, step 0,
or the initialization step.
States of Outputs Based on Destination Steps
If the SDS instruction enters: Then outputs:
an error step are set as defined in that step
step 0 reset to off
initialization step stay in the last state
Message Generation
The SDS instruction generates an error message or status message when it
enters a new step which has its message bit enabled. This message is
displayed on the operator interface terminal and/or an annunciator panel if
you so specify. (The figure on page 1–4 shows where you can turn
messages on and off using the [F7] key.) Error messages are cleared from
the display device (operator interface terminal or annunciator panel) only
when the instruction goes to step 0. All other types of messages are
cleared when the instruction moves to the next step.