193
Basic Ladder Diagrams
Section 4-3
Again, this diagram can be redrawn as follows to simplify program structure
and coding and to save memory space.
The next and final example may at first appear very complicated but can be
coded using only two logic block instructions. The diagram appears as follows:
The first logic block instruction is used to combine the execution conditions
resulting from blocks a and b, and the second one is to combine the execution
condition of block c with the execution condition resulting from the normally
closed condition assigned IR 00003. The rest of the diagram can be coded
with OR, AND, and AND NOT instructions. The logical flow for this and the
resulting code are shown below.
00006
00007
LR 0000
00005
00001
00002
00003
00004
00000
Address
Instruction
Operands
00000
LD
00006
00001
AND
00007
00002
OR
00005
00003
AND
00003
00004
AND
00004
00005
LD
00001
00006
AND
00002
00007
OR LD
--
00008
AND
00000
00009
OUT
LR
0000
00000
00001
10000
00002
00003
01000
01001
00004
00005
10000
00006
Block c
Block b
Block a