55
lowed by the one to combine the execution condition resulting from the first
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-
ever, 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
00503
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 00503
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,
Complicated Diagrams
Basic Ladder Diagrams Section 4-3
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