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When an INTERLOCK instruction is placed before a section of a ladder pro-
gram, the execution condition for the INTERLOCK instruction will control the ex-
ecution of all instruction up to the next INTERLOCK CLEAR instruction. If the
execution condition for the INTERLOCK instruction is OFF, all right-hand in-
structions through the next INTERLOCK CLEAR instruction will be executed
with OFF execution conditions to reset the entire section of the ladder diagram.
The effect that this has on particular instructions is described in
5-10 INTER-
LOCK and INTERLOCK CLEAR – IL(02) and ILC(03).
Diagram B can also be corrected with an interlock. Here, the conditions leading
up to the branching point are placed on an instruction line for the INTERLOCK
instruction, all of lines leading from the branching point are written as separate
instruction lines, and another instruction line is added for the INTERLOCK
CLEAR instruction. No conditions are allowed on the instruction line for INTER-
LOCK CLEAR. Note that neither INTERLOCK nor INTERLOCK CLEAR re-
quires an operand.
Instruction 1
00002
00000
Instruction 2
00001
ILC(03)
IL(02)
Address Instruction Operands
00000 LD 00000
00001 IL(02) ---
00002 LD 00001
00003 Instruction 1
00004 LD 00002
00005 Instruction 2
00006 ILC(03) ---
If IR 00000 is ON in the revised version of diagram B, above, the status of IR
00001 and that of IR 00002 would determine the execution conditions for in-
structions 1 and 2, respectively. Because IR 00000 is ON, this would produce the
same results as ANDing the status of each of these bits. If IR 00000 is OFF, the
INTERLOCK instruction would produce an OFF execution condition for instruc-
tions 1 and 2 and then execution would continue with the instruction line follow-
ing the INTERLOCK CLEAR instruction.
As shown in the following diagram, more than one INTERLOCK instruction can
be used within one instruction block; each is effective through the next INTER-
LOCK CLEAR instruction.
Instruction 1
00000
Instruction 2
00001
ILC(03)
IL(02)
00004
Instruction 3
Instruction 4
00006
00005
00003
00002
IL(02)
Address Instruction Operands
00000 LD 00000
00001 IL(02) ---
00002 LD 00001
00003 Instruction 1
00004 LD 00002
00005 IL(02) ---
00006 LD 00003
00007 AND NOT 00004
00008 Instruction 2
00009 LD 00005
00010 Instruction 3
00011 LD 00006
00012 Instruction 4
00013 ILC(03) ---
Inputting, Modifying, and Checking the Program Section 4-7