TSC80251 TEMIC [TEMIC Semiconductors], TSC80251 Datasheet - Page 205

• Manufacturer Part Number: TSC80251
• Manufacturer: TEMIC [TEMIC Semiconductors]

5.160
TSC80251
SUBB A,<src-byte>
Function:
Subtract with borrow
Description:
SUBB subtracts the specified variable and the CY flag together from the accumulator, leaving the result in the
accumulator. SUBB sets the CY (borrow) flag if a borrow is needed for bit 7 and clears CY otherwise. (If CY was set
before executing a SUBB instruction, this indicates that a borrow was needed for the previous step in a multiple
precision subtraction, so the CY flag is subtracted from the accumulator along with the source operand.) AC is set if
a borrow is needed for bit 3 and cleared otherwise. OV is set if a borrow is needed into bit 6, but not into bit 7, or into
bit 7, but not bit 6.
When subtracting signed integers the OV flag indicates a negative number produced when a negative value is
subtracted from a positive value or a positive result when a positive number is subtracted from a negative number.
Bit 6 and bit 7 in this description refer to the most significant byte of the operand (8, 16 or 32 bit)
The source operand allows four addressing modes: register, direct, register–indirect or immediate.
Example :
The accumulator contains 0C9h (11001001B), register 2 contains 54h (01010100B), and the CY flag is set. After
executing the instruction SUBB A,R2 the accumulator contains 74h (01110100B), the CY and AC flags are clear, and
the OV flag is set.Notice that 0C9h minus 54h is 75h. The difference between this and the above result is due to the
CY (borrow) flag being set before the operation. If the state of the carry is not known before starting a single or
multiple–precision subtraction, it should be explicitly cleared by a CLR CY instruction.
SUBB A,#data
[Encoding]
SUBB A,dir8
[Encoding]
FLAGS :
Hex Code in:
Binary Mode = [Encoding]
Source Mode = [Encoding]
1001
1001
CY
0100
0101
AC
addr7-addr0
immed data
OV
Operation:
SUBB
(A)
(A) - (CY) - #data
N
Rev. C – May 7, 1999
Z