Rockwell Automation D64046.5.1 U MNL WIN DDMC - Manual (Page 39)

Configuring SDS Instructions
Chapter 4
4-3
Graphic Example of Transitional Equations
LS ON–> OFF
PB ON–> OFF
LS2 ON–>OFF
LS3 0FF–> ON
Step
1
Step
2
Step
3
Step
4
This type of SDS instruction operates from a series of step tables that define
output states for each step, and input transitions as either normal or abnormal.
Normal transitions direct the SDS instruction to another step; abnormal
transitions can cause the instruction to send a message to the operator interface
terminal, where DDMC32 software automatically assembles and displays the
appropriate diagnostic message.
The SDS instruction also allows you to implement “shadow mode” diagnostics.
In “shadow mode” control is placed in the ladder logic; the SDS simply
monitors the I/O performing the control and performs diagnostics on that I/O.
Combinatorial Equations
In addition to the transitional equation, the SDS instruction can also use
combinatorial conditions or equations which allow for the ANDing of inputs in
addition to the OR function (as seen in transitional equations).
You can also use the NOT function, although it is not as true an operand as the
AND function is. The NOT function is concerned with input state only. This
allows complex combinations or mechanisms that are not easily defined by
individual state transitions to be accommodated more easily within the SDS
framework with a minimum number of steps. See the next page for an example
of what is meant by combinatorial equations.