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The following diagram contains only two logic blocks as shown. It is not neces-
sary to further separate block b components, because it can be coded directly
using only AND and OR.
00000 00001
00002 00003
00201
00501
00004
Block
a
Block
b
Address
Instruction
Operands
00000
LD
00000
00001
AND NOT
00001
00002
LD
00002
00003
AND
00003
00004
OR
00201
00005
OR
00004
00006
AND LD
—
00007
OUT
00501
Although the following diagram is similar to the one above, block b in the diagram
below cannot be coded without separating it into two blocks combined with OR
LOAD. In this example, the three blocks have been coded first and then OR
LOAD has been used to combine the last two blocks, followed by AND LOAD to
combine the execution condition produced by the OR LOAD with the execution
condition of block a.
When coding the logic block instructions together at the end of the logic blocks
they are combining, they must, as shown below, be coded in reverse order, i.e.,
the logic block instruction for the last two blocks is coded first, followed by the
one to combine the execution condition resulting from the first logic block in-
struction and the execution condition of the logic block third from the end, and on
back to the first logic block that is being combined.
00000 00001
00002 00003
00502
00004 00202
Block
a
Block
b
Block
b2
Block
b1
Address
Instruction
Operands
00000
LD NOT
00000
00001
AND
00001
00002
LD
00002
00003
AND NOT
00003
00004
LD NOT
00004
00005
AND
00202
00006
OR LD
—
00007
AND LD
—
00008
OUT
00502
Complicated Diagrams
When determining what logic block instructions will be required to code a dia-
gram, it is sometimes necessary to break the diagram into large blocks and then
continue breaking the large blocks down until logic blocks that can be coded
without logic block instructions have been formed. These blocks are then coded,
combining the small blocks first, and then combining the larger blocks. Either
AND LOAD or OR LOAD is used to combine the blocks, i.e., AND LOAD or OR
LOAD always combines the last two execution conditions that existed, regard-
less of whether the execution conditions resulted from a single condition, from
logic blocks, or from previous logic block instructions.
Basic Ladder Diagrams
Section 4-4