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4-8-1 DIFFERENTIATE UP and DIFFERENTIATE DOWN
DIFFERENTIATE UP and DIFFERENTIATE DOWN instructions are used to
turn the operand bit ON for one cycle at a time. The DIFFERENTIATE UP
instruction turns ON the operand bit for one cycle after the execution condition
for it goes from OFF to ON; the DIFFERENTIATE DOWN instruction turns ON
the operand bit for one cycle after the execution condition for it goes from ON to
OFF. Both of these instructions require only one line of mnemonic code.
00000
00001
DIFU(13) 00200
DIFD(14) 00201
Address Instruction Operands
00000 LD 00000
00001 DIFU(13) 00200
Address Instruction Operands
00000 LD 00001
00001 DIFD(14) 00201
Here, IR 00200 will be turned ON for one cycle after IR 00000 goes ON. The next
time DIFU(13) 00200 is executed, IR 00200 will be turned OFF, regardless of the
status of IR 00000. With the DIFFERENTIATE DOWN instruction, IR 00201 will
be turned ON for one cycle after IR 00001 goes OFF (IR 00201 will be kept OFF
until then), and will be turned OFF the next time DIFD(14) 00201 is executed.
4-8-2 KEEP
The KEEP instruction is used to maintain the status of the operand bit based on
two execution conditions. To do this, the KEEP instruction is connected to two
instruction lines. When the execution condition at the end of the first instruction
line is ON, the operand bit of the KEEP instruction is turned ON. When the
execution condition at the end of the second instruction line is ON, the operand
bit of the KEEP instruction is turned OFF. The operand bit for the KEEP instruc-
tion will maintain its ON or OFF status even if it is located in an interlocked sec-
tion of the diagram.
In the following example, HR 0000 will be turned ON when IR 00002 is ON and IR
00003 is OFF. HR 0000 will then remain ON until either IR 00004 or IR 00005
turns ON. With KEEP, as with all instructions requiring more than one instruction
line, the instruction lines are coded first before the instruction that they control.
00002
00004
00003
00005
R: reset input
S: set input
KEEP(11)
HR 0000
Address Instruction Operands
00000 LD 00002
00001 AND NOT 00003
00002 LD 00004
00003 OR 00005
00004 KEEP(11) HR 0000
4-8-3 Self-maintaining Bits (Seal)
Although the KEEP instruction can be used to create self-maintaining bits, it is
sometimes necessary to create self-maintaining bits in another way so that they
can be turned OFF when in an interlocked section of a program.
Controlling Bit Status Section 4-8