Samsung KS57C2308 manual Skip Condition Flags SC2, SC1, SC0, Carry Flag C

ADDRESS SPACES KS57C2308/P2308/C2316/P2316

SKIP CONDITION FLAGS (SC2, SC1, SC0)

The skip condition flags SC2, SC1, and SC0 in the PSW indicate the current program skip conditions and are set and reset automatically during program execution. Skip condition flags can only be addressed by 8-bit read instructions. Direct manipulation of the SC2, SC1, and SC0 bits is not allowed.

CARRY FLAG (C)

The carry flag is used to save the result of an overflow or borrow when executing arithmetic instructions involving a carry (ADC, SBC). The carry flag can also be used as a 1-bit accumulator for performing Boolean operations involving bit-addressed data memory.

If an overflow or borrow condition occurs when executing arithmetic instructions with carry (ADC, SBC), the carry flag is set to "1". Otherwise, its value is "0". When a RESET occurs, the current value of the carry flag is retained during power-down mode, but when normal operating mode resumes, its value is undefined.

The carry flag can be directly manipulated by predefined set of 1-bit read/write instructions, independent of other bits in the PSW. Only the ADC and SBC instructions, and the instructions listed in Table 2-7, affect the carry flag.

Table 2-7. Valid Carry Flag Manipulation Instructions

Operation Type	Instructions	Carry Flag Manipulation
Direct manipulation	SCF	Set carry flag to "1"
	RCF	Clear carry flag to "0" (reset carry flag)
	CCF	Invert carry flag value (complement carry flag)
	BTST C	Test carry and skip if C = "1"
Bit transfer	LDB (operand) (1),C	Load carry flag value to the specified bit
	LDB C,(operand) (1)	Load contents of the specified bit to carry flag
Boolean manipulation	BAND C,(operand) (1)	AND the specified bit with contents of carry flag and save
		the result to the carry flag
	BOR C,(operand) (1)	OR the specified bit with contents of carry flag and save
		the result to the carry flag
	BXOR C,(operand) (1)	XOR the specified bit with contents of carry flag and save
		the result to the carry flag
Interrupt routine	INTn (2)	Save carry flag to stack with other PSW bits
Return from interrupt	IRET	Restore carry flag from stack with other PSW bits

NOTES:

1.The operand has three bit addressing formats: mema.a, memb.@L, and @H + DA.b.

2.“INTn” refers to the specific interrupt being executed and is not an instruction.

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