57
last two blocks and working backward. The OR LOAD at program address
00008 combines blocks blocks d and e, the following AND LOAD combines
the resulting execution condition with that of block c, etc.
LR 0000
00000
00003
00004
00006 00007
00001 00002
00005
Block e
Block dBlock c
Block b
Block a
Address Instruction Operands
Blocks d and e
Block c with result of above
Block b with result of above
Block a with result of above
00000 LD 00000
00001 LD 00001
00002 AND 00002
00003 LD 00003
00004 AND 00004
00005 LD 00005
00006 LD 00006
00007 AND 00007
00008 OR LD --
00009 AND LD --
00010 OR LD --
00011 AND LD --
00012 OUT LR 0000
Again, this diagram can be redrawn as follows to simplify program structure
and coding and to save memory space.
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
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 fol-
lows:
00000 00001
00500
00002 00003
01000 01001
00004 00005
00500
00006
Block cBlock b
Block a
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 execu-
Basic Ladder Diagrams Section 4-3
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