Selectron LD-007 Manual de Instruções descarregar pdf (Página 61)

described later. The END instruction requires no operands and no conditions

can be placed on the same instruction line with it.

Instruction

00000 00001

END(01)

Program execution

ends here.

Address Instruction Operands

00000 LD 00000

00001 AND NOT 00001

00002 Instruction

00003 END(01) ---

If there is no END instruction anywhere in the program, the program will not

be executed at all.

Now you have all of the instructions required to write simple input-output pro-

grams. Before we finish with ladder diagram basic and go onto inputting the

program into the PC, let’s look at logic block instruction (AND LOAD and OR

LOAD), which are sometimes necessary even with simple diagrams.

4-3-6 Logic Block Instructions

Logic block instructions do not correspond to specific conditions on the lad-

der diagram; rather, they describe relationships between logic blocks. The

AND LOAD instruction logically ANDs the execution conditions produced by

two logic blocks. The OR LOAD instruction logically ORs the execution condi-

tions produced by two logic blocks.

Although simple in appearance, the diagram below requires an AND LOAD

instruction.

Instruction

00002

00003

00000

00001

Address Instruction Operands

00000 LD 00000

00001 OR 00001

00002 LD 00002

00003 OR NOT 00003

00004 AND LD ---

The two logic blocks are indicated by dotted lines. Studying this example

shows that an ON execution condition will be produced when: either of the

conditions in the left logic block is ON (i.e., when either IR 00000 or IR 00001

is ON), and when either of the conditions in the right logic block is ON (i.e.,

when either IR 00002 is ON or IR 00003 is OFF).

The above ladder diagram cannot, however, be converted to mnemonic code

using AND and OR instructions alone. If an AND between IR 00002 and the

results of an OR between IR 00000 and IR 00001 is attempted, the OR NOT

between IR 00002 and IR 00003 is lost and the OR NOT ends up being an

AND LOAD

Basic Ladder Diagrams Section 4-3

1 2 ... 56 57 58 59 60 61 62 63 64 65 66 ... 367 368

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