91
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. INTERLOCK and INTERLOCK CLEAR does not use operands.
Address Instruction
00000 LD 000000
00001 IL(002) ---
00002 LD 000001
00003 Instruction 1
00004 LD 000002
00005 Instruction 2
00006 ILC(003) ---
Operands
Instruction 1
Instruction 2
(002)
IL
0000
00
0000
01
0000
02
(003)
ILC
If CIO 000000 is ON in the revised version of diagram B, above, the status of
CIO 000001 and that of CIO 000002 would determine the execution conditions
for instructions 1 and 2, respectively. Because CIO 000000 is ON, this would
produce the same results as ANDing the status of each of these bits. If
CIO 000000 is OFF, the INTERLOCK instruction would produce an OFF execu-
tion condition for instructions 1 and 2 and then execution would continue with the
instruction line following the INTERLOCK CLEAR instruction.
As shown below, multiple INTERLOCK instructions can be used in one instruc-
tion block; each is effective through the next INTERLOCK CLEAR instruction.
Address Instruction
00000 LD 000000
00001 IL(002) ---
00002 LD 000001
00003 Instruction 1
00004 LD 000002
00005 IL(002) ---
00006 LD 000003
00007 AND NOT 000004
00008 Instruction 2
00009 LD 000005
00010 Instruction 3
00011 LD 000006
00012 Instruction 4
00013 ILC(003) ---
Operands
Instruction 4
Instruction 1
Instruction 2
Instruction 3
(002)
IL
(003)
ILC
0000
00
(002)
IL
0000
01
0000
02
0000
03
0000
04
0000
05
0000
06
If CIO 000000 in the above diagram is OFF (i.e., if the execution condition for the
first INTERLOCK instruction is OFF), instructions 1 through 4 would be
executed with OFF execution conditions and execution would move to the
instruction following the INTERLOCK CLEAR instruction. If CIO 000000 is ON,
the status of CIO 000001 would be loaded as the execution condition for instruc-
tion 1 and then the status of CIO 000002 would be loaded to form the execution
condition for the second INTERLOCK instruction. If CIO 000002 is OFF, instruc-
tions 2 through 4 will be executed with OFF execution conditions. If CIO 000002
is ON, CIO 000003, CIO 000005, and CIO 000006 will determine the first execu-
tion condition in new instruction lines.
Branching Instruction Lines Section 4-5
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