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36
μ
PD75518(A)
(1) Carry flag (CY)
The carry flag is a 1-bit flag used to store overflow or underflow occurrence information when an arithmetic
operation with a carry (ADDC, SUBC) is executed.
The carry flag also has the function of a bit accumulator, and therefore can be used to store the result of
a Boolean operation performed on the CY and bit at a specified data memory bit address.
The carry flag is manipulated using special instructions, independently of the other PSW bits.
A RESET signal occurrence causes the carry flag to be undefined.
Table 3-3 Carry Flag Manipulation Instructions
Remark
mem*.bit represents the following three addressing modes:
fmem.bit
pmem.@L
@H+mem.bit
Example
Bit 3 at address 3FH is ANDed with P33, then the result is output to P50.
MOV
H, #3H
; Set high-order 4 bits in register H
MOV1
CY, @H+0FH.3 ; CY
←
Bit 3 at 3FH
AND1
CY, PORT3.3
; CY
←
CY P33
MOV1
PORT5.0, CY
; P50
←
CY
(2) Skip flags (SK2, SK1, SK0)
The skip flags are used to store skip status, and are automatically set or reset when the CPU executes an
instruction.
The user cannot directly manipulate these flags as operands.
(3) Interrupt status flag (IST1, IST0)
The interrupt status flag is a 2-bit flag used to store the status of processing being performed. (For detailed
information, see
Table 5-3
.)
Instruction dedicated to
carry flag manipulation
Bit transfer instruction
Bit Boolean instruction
Interrupt handling
SET1 CY
CLR1 CY
NOT1 CY
SKT CY
MOV1 mem*.bit,CY
MOV1 CY,mem*.bit
AND1 CY,mem*.bit
OR1 CY,mem*.bit
XOR1 CY,mem*.bit
Interrupt execution
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Restores CY together with the other PSW bits from stack memory.
RETI
Sets CY to 1.
Clears CY to 0.
Inverts the contents of CY.
Skips if CY is set to 1.
Transfers the contents of CY to a specified bit.
Transfers the contents of a specified bit to CY.
ANDs, ORs, or XORs CY with the contents of a specified bit, then
sets the result in CY.
Saves CY and all other PSW bits to stack memory in parallel.
Carry flag operation/processing
Instruction (mnemonic)