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Step Instructions Section 5-14
Execution of a step is completed either by execution of the next SNXT(09) or
by turning OFF the control bit for the step (see example 3 below). When the
step is completed, all of the IR and HR bits in the step are turned OFF and all
timers in the step are reset to their SVs. Counters, shift registers, and bits
used in KEEP(11) maintain status. Two simple steps are shown below.
Steps can be programmed in consecutively. Each step must start with
STEP(08) and generally ends with SNXT(09) (see example 3, below, for an
exception). When steps are programmed in series, three types of execution
are possible: sequential, branching, or parallel. The execution conditions for,
and the positioning of, SNXT(09) determine how the steps are executed. The
three examples given below demonstrate these three types of step execution.
Precautions Interlocks, jumps, SBN(92), and END(01) cannot be used within step pro-
grams.
Bits used as control bits must not be used anywhere else in the program
unless they are being used to control the operation of the step (see example
3, below). All control bits must be in the same word and must be consecutive.
If IR or LR bits are used for control bits, their status will be lost during any
power interruption. If it is necessary to maintain status to resume execution at
the same step, HR bits must be used.
SNXT(09) LR 1500
STEP(08) LR 1500
00000
Step controlled by LR 1500
SNXT(09) LR 1501
STEP(08) LR 1501
00001
Step controlled by LR 1501
SNXT(09) LR 1502
STEP(08)
00002
Starts step execution
Ends step execution
1st step
2nd step
Address Instruction OperandsAddress Instruction Operands
00000 LD 00000
00001 SNXT(09) LR 1500
00002 STEP(08) LR 1500
Step controlled by LR 1500.
00100 LD 00001
00101 SNXT(09) LR 1501
00102 STEP(08) LR 1501
Step controlled by LR 1501.
00200 LD 00002
00201 SNXT(09) LR 1502
00202 STEP(08) ---
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