2-171
2 Instructions
CP1E CPU Unit Instructions Reference Manual(W483)
Symbol Math Instructions
2
–C/–CL
Function
–C
–C(412) subtracts the binary values in Su and CY from Mi, and outputs the result to R. When the result
is negative, it is output to R as a 2’s complement.
–CL
–CL(413) subtracts the binary values in Su and Su+1 and CY from Mi and Mi+1, and outputs the result
to R, R+1. When the result is negative, it is output to R, R+1 as a 2’s complement.
Hint
•To clear the Carry Flag (CY), execute the Clear Carry (CLC(041)) instruction.
• 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 follows:
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.
Sample program
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 num-
ber, 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 subtraction is negative.
–
CY
R
CY
Mi
Su
(Signed binary)
(Signed binary)
(Signed binary)
CY will turn ON
when there is a
borrow.
–
R+1
CY
R
CY
Mi+1
Su+1
Mi
Su
(Signed binary)
(Signed binary)
(Signed binary)
CY will turn ON
when there is a
borrow.
−C
D100
D110
D120
0.00
When CIO 0.00 is ON in the following example, D110 and CY will be
subtracted from D100 as 4-digit signed binary values and the result will
be output to D120.
−CL
D100
D110
D120
0.00
When CIO 0.00 is ON in the following example, D111, D110 and CY will be
subtracted from D101 and D100 as 8-digit signed binary values, and the
result will be output to D121 and D120.