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Symbol Math Instructions Section 3-10
If the result of the subtraction is a negative number (Mi<Su or Mi+1, Mi
<Su+1, Su), the result is output as a 2’s complement. The Carry Flag (CY) will
turn ON. To convert the 2’s complement to the true number, a program which
subtracts the result from 0 is necessary, as an input condition of the Carry
Flag (CY). The Carry Flag turning ON thus indicates that the result of the sub-
traction is negative.
Note 2’s Complement
A 2’s complement is the value obtained by subtracting each binary digit from 1
and adding one to the result.
Example: The 2’s complement for the binary number 1101 is as follows:
1111 (F hex) – 1101 (D hex) + 1 (1 hex) = 0011 (3 hex).
Example: The 2’s complement for the 4-digit hexadecimal number 3039 is as
follows:
FFFF hex – 3039 hex + 0001 hex = CFC7 hex.
Accordingly, the 2’s complement for the 4-digit hexadecimal value “a” is as fol-
lows:
FFFF hex – a hex + 0001 hex = b hex.
And to obtain the true number “a” hex from the 2’s complement “b” hex:
a hex + 10000 hex – b hex.
Example: To obtain the true number from the 2’s complement CFC& hex:
10000 hex – CFC7 hex = 3039 hex.
3-10-13 BCD SUBTRACT WITHOUT CARRY: –B(414)
Purpose Subtracts 4-digit (single-word) BCD data and/or constants.
Ladder Symbol
Variations
Applicable Program Areas
Operand Specifications
–B(414)
R
Mi
Su
Mi: Minuend word
Su: Subtrahend word
R: Result word
Variations Executed Each Cycle for ON Condition –B(414)
Executed Once for Upward Differentiation @–B(414)
Executed Once for Downward Differentiation Not supported.
Immediate Refreshing Specification Not supported.
Block program areas Step program areas Subroutines Interrupt tasks
OK OK OK OK
Area Mi Su R
CIO Area CIO 0 to CIO 6143
Work Area W0 to W511
Holding Bit Area H0 to H511
Auxiliary Bit Area A0 to A959 A448 to A959
Timer Area T0000 to T4095
Counter Area C0000 to C4095
DM Area D0 to D32767
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