6-3
Section
Basic Ladder Diagrams
346
The following diagram must be broken down into two blocks and each of these
then broken into two blocks before it can be coded. As shown below, blocks a
and b require an AND LOAD. Before AND LOAD can be used, however, OR
LOAD must be used to combine the top and bottom blocks on both sides, i.e., to
combine a1 and a2; b1 and b2.
00000 00001
00004 00005
20003
Block
a
Block
b
00006 00007
Block
b2
Block
b1
00002 00003
Block
a2
Block
a1
Blocks a1 and a2
Blocks b1 and b2
Blocks a and b
Address
Instruction
Operands
00000
LD
00000
00001
AND NOT
00001
00002
LD NOT
00002
00003
AND
00003
00004
OR LD
—
00005
LD
00004
00006
AND
00005
00007
LD
00006
00008
AND
00007
00009
OR LD
—
00010
AND LD
—
00011
OUT
20003
The following type of diagram can be coded easily if each block is coded in order:
first top to bottom and then left to right. In the following diagram, blocks a and b
would be combined using AND LOAD as shown above, and then block c would
be coded and a second AND LOAD would be used to combined it with the execu-
tion condition from the first AND LOAD. Then block d would be coded, a third
AND LOAD would be used to combine the execution condition from block d with
the execution condition from the second AND LOAD, and so on through to block
n.
Block
a
Block
b
20000
Block
n
Block
c