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4-7-7 Branching Instruction Lines
When an instruction line branches into two or more lines, it is sometimes neces-
sary to use either interlocks or TR bits to maintain the execution condition that
existed at a branching point. This is because instruction lines are executed
across to a right-hand instruction before returning to the branching point to ex-
ecute instructions on a branch line. If a condition exists on any of the instruction
lines after the branching point, the execution condition could change during this
time making proper execution impossible. The following diagrams illustrate this.
In both diagrams, instruction 1 is executed before returning to the branching
point and moving on to the branch line leading to instruction 2.
Instruction 1
00002
00000
Instruction 2
Branching
point
Instruction 1
00002
00000
Instruction 2
Branching
point
Diagram B: Incorrect Operation
Diagram A: Correct Operation
00001
Address
Instruction
Operands
00000
LD
00000
00001
Instruction 1
00002
AND
00002
00003
Instruction 2
Address
Instruction
Operands
00000
LD
00000
00001
AND
00001
00002
Instruction 1
00003
AND
00002
00004
Instruction 2
If, as shown in diagram A, the execution condition that existed at the branching
point cannot be changed before returning to the branch line (instructions at the
far right do not change the execution condition), then the branch line will be ex-
ecuted correctly and no special programming measure is required.
If, as shown in diagram B, a condition exists between the branching point and the
last instruction on the top instruction line, the execution condition at the branch-
ing point and the execution condition after completing the top instruction line will
sometimes be different, making it impossible to ensure correct execution of the
branch line.
There are two means of programming branching programs to preserve the ex-
ecution condition. One is to use TR bits; the other, to use interlocks
(IL(02)/IL(03)).
TR Bits
The TR area provides eight bits, TR 0 through TR 7, that can be used to tempo-
rarily preserve execution conditions. If a TR bit is placed at a branching point, the
current execution condition will be stored at the designated TR bit. When return-
ing to the branching point, the TR bit restores the execution status that was
saved when the branching point was first reached in program execution.
Inputting, Modifying, and Checking the Program
Section 4-7
Содержание SYSMAC C200HS
Страница 1: ...Cat No W235 E1 05 C200HS SYSMAC Programmable Controllers...
Страница 2: ...C200HS Programmable Controllers Operation Manual Revised February 2002...
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Страница 379: ...371 SR word Corresponding key s Bit 279 03 04 05 3 06 07 VER 08 09 Monitoring Operation and Modifying Data Section 7 1...
Страница 470: ...468 Programmer Program Date Page Word Contents Notes Word Contents Notes Data Storage...
Страница 471: ...469 Programmer Program Date Page TC address T or C Set value Notes TC address T or C Set value Notes Timers and Counters...