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2 Instructions
2-176
CP1E CPU Unit Instructions Reference Manual(W483)
Function
–BC
–BC(416) subtracts BCD values in Su and CY from Mi and outputs the result to R. If the result is nega-
tive, it is output to R as a 10’s complement.
–BCL
–BCL(417)subtracts the BCD values in Su, Su+1, and CY from Mi and Mi+1 and outputs the result to R,
R+1. If the result is negative, it is output to R, R+1 as a 10’s complement.
Hint
• To clear the Carry Flay (CY), execute the Clear Carry (CLC(041)) instruction.
• 10’s Complement
A 10’s complement is the value obtained by subtracting each digit from 9 and adding one to the
result. For example, the 10’s complement for 7556 is calculated as follows: 9999 - 7556 + 1 = 2444.
For a four digit number, the 10’s complement of A is 9999 – A + 1 = B. To obtain the true number from
the 10’s complement B: A = 10000 – B. For example, to obtain the true number from the 10’s comple-
ment 2444: 10000 – 2444 = 7556.
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 10’s complement. The Carry Flag (CY) will turn ON. To convert the 10’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 subtraction is negative.
–
CY
RCY
(BCD)
(BCD)
(BCD)
Mi
Su
CY will turn ON
when there is a
borrow.
–
R+1
CY
RCY
(BCD)
(BCD)
(BCD)
Mi+1
Su+1
Mi
Su
CY will turn ON
when there is a
borrow.
−BC
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 BCD values, and the
result will be output to D120.
−BCL
D100
D110
D120
0.00
When CIO 0.00 is ON in thefollowing example, D111, D110,
and CY will be subtracted from D101 and D100 as 8-digit
BCD values, and the result will be output to D121 and D120.