204
5-19 BCD Calculations
The BCD calculation instructions – INC(38), DEC(39), ADD(30), ADDL(54),
SUB(31), SUBL(55), MUL(32), MULL(56), DIV(33), DIVL(57), FDIV(79), and
ROOT(72) – all perform arithmetic operations on BCD data.
For
INC(38) and DEC(39) the source and result words are the same. That is, the
content
of the source word is overwritten with the instruction result. All other
in
-
structions
change only the content of the words in which results are placed, i.e.,
the
contents of source words are
the same before and after execution of any of
the other BCD calculation instructions.
STC(40) and CLC(41), which set and clear the carry flag, are included in this
group
because most of the BCD operations make use of
the Carry Flag (CY) in
their results. Binary calculations and shift operations also use CY.
The
addition and subtraction instructions include CY in the calculation as well as
in
the result. Be sure to clear
CY if its previous status is not required in the calcu
-
lation, and to use the result placed in CY
, if required, before it is changed by exe
-
cution of any other instruction.
5-19-1 INCREMENT – INC(38)
Wd: Increment word (BCD)
IR, SR, AR, DM, HR, LR
Ladder Symbols Operand Data Areas
INC(38)
Wd
@INC(38)
Wd
Description When
the execution condition is OFF
, INC(38) is not executed. When the execu
-
tion condition is ON, INC(38) increments Wd, without affecting Carry (CY).
Flags ER: Wd is not BCD
Indirectly
addressed DM word
is non-existent. (Content of
∗
DM word is
not BCD, or the DM area boundary has been exceeded.)
EQ: ON when the incremented result is 0.
5-19-2 DECREMENT – DEC(39)
Wd: Decrement word (BCD)
IR, SR, AR, DM, HR, LR
Ladder Symbols Operand Data Areas
DEC(39)
Wd
@DEC(39)
Wd
Description When
the execution condition is OFF
, DEC(39) is not executed. When the exe
-
cution
condition is ON,
DEC(39) decrements Wd, without af
fecting CY
. DEC(39)
works
the same way as INC(38) except
that it decrements the value instead of
incrementing it.
Flags ER: Wd is not BCD
Indirectly
addressed DM word
is non-existent. (Content of
∗
DM word is
not BCD, or the DM area boundary has been exceeded.)
EQ: ON when the decremented result is 0.
BCD Calculations Section 5-19
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