====== Step Control ======

S Registers are used for step control. Step control arguments must follow
the following format.

{{ :cubloc:stepset_stepout:stepcontrol.png?nolink |}}

Step control can be performed in two ways: "Normal Step" and "Reverse
Step". STEPSET is used for "Normal Step".

===== STEPSET =====

STEPSET turns ON the current step, but only if the previous step is ON.
STEPSET is processed one step at a time, in sequence, according to the step
number. For example, in the ladder above, when P1 turns ON, S0:2 is
turned ON, but only if S0:1 is ON. 

{{ :cubloc:stepset_stepout:stepset1.png?nolink |}}

After S0:2 turns ON, S0:1 is turns OFF.
When P2 turns ON, S0:0 is turned ON and all other steps are turned OFF.
S0:0, or step 0, is used to reset. All other steps are processed in order.

{{ :cubloc:stepset_stepout:stepset2.png?nolink |}}

===== STEPOUT =====

STEPOUT differs from STEPSET in two ways. First, it is not evaluated in
sequence, and second, when a step is turned ON, it remains in that state
regardless of its input condition. When using STEP OUT and a step is
turned ON, all other steps are turned OFF, so only one step is ON at any
given time.

{{ :cubloc:stepset_stepout:stepout.png?nolink |}}

In the ladder above, when P1 turns ON, S0:2 will turn ON. When P0 turns
on S0:1 turns ON, and S0:2 turns OFF and S0:1 turns ON. When PO turns
OFF, S0:1 is unchanged as each step, when turned ON, remains ON
regardless of its input condition. Finally when P2 turns ON, S0:0 turns ON
and S0:1 turns OFF.

{{ :cubloc:stepset_stepout:stepout2.png?nolink |}}

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