200
gram so that it is executed before the program reaches the step it starts. It
can be used at different locations before the step to control the step accord-
ing to two different execution conditions (see example 2, below). Any step in
the program that has not been started with SNXT(09) will not be executed.
Once SNXT(09) is used in the program, step execution will continue until
STEP(08) is executed without a control bit. STEP(08) without a control bit
must be preceded by SNXT(09) with a dummy control bit. The dummy con-
trol bit may be any unused IR or HR bit. It cannot be a control bit used in a
STEP(08).
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.
SNXT(09) 20200
STEP(08) 20200
00000
Step controlled by 20200
SNXT(09) 20201
STEP(08) 20201
00001
Step controlled by 20201
SNXT(09) 20202
STEP(08)
00002
Starts step execution
Ends step execution
1st step
2nd step
Address
Instruction
Operands
Address
Instruction
Operands
00000
LD
00000
00001
SNXT(09)
20200
00002
STEP(08)
20200
Step controlled by 20200.
00100
LD
00001
00101
SNXT(09)
20201
00102
STEP(08)
20201
Step controlled by 20201.
00200
LD
00002
00201
SNXT(09)
20202
00202
STEP(08)
---
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 execu-
tion.
Step Instructions
Section 5-22
Содержание SYSMAC C1000H
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