53
logic block instruction 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
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, regardless of whether the execution conditions resulted from a
single condition, from logic blocks, or from previous logic block instructions.
When working with complicated diagrams, blocks will ultimately be coded
starting at the top left and moving down before moving across. This will gen-
erally mean that, when there might be a choice, OR LOAD will be coded be-
fore AND LOAD.
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, how-
Complicated Diagrams
Basic Ladder Diagrams
Section 4-3
