Samsung S3C84E5 user manual Flag Descriptions

S3C84E5/C84E9/P84E9 INSTRUCTION SET

FLAG DESCRIPTIONS

C Carry Flag (FLAGS.7)

The C flag is set to "1" if the result from an arithmetic operation generates a carry-out from or a borrow to the bit 7 position (MSB). After rotate and shift operations have been performed, it contains the last value shifted out of the specified register. Program instructions can set, clear, or complement the carry flag.

Z Zero Flag (FLAGS.6)

For arithmetic and logic operations, the Z flag is set to "1" if the result of the operation is zero. In operations that test register bits, and in shift and rotate operations, the Z flag is set to "1" if the result is logic zero.

S Sign Flag (FLAGS.5)

Following arithmetic, logic, rotate, or shift operations, the sign bit identifies the state of the MSB of the result. A logic zero indicates a positive number and a logic one indicates a negative number.

V Overflow Flag (FLAGS.4)

The V flag is set to "1" when the result of a two's-complement operation is greater than + 127 or less than – 128. It is cleared to "0" after a logic operation has been performed.

D Decimal Adjust Flag (FLAGS.3)

The DA bit is used to specify what type of instruction was executed last during BCD operations so that a subsequent decimal adjust operation can execute correctly. The DA bit is not usually accessed by programmers, and it cannot be addressed as a test condition.

H Half-Carry Flag (FLAGS.2)

The H bit is set to "1" whenever an addition generates a carry-out of bit 3, or when a subtraction borrows out of bit 4. It is used by the Decimal Adjust (DA) instruction to convert the binary result of a previous addition or subtraction into the correct decimal (BCD) result. The H flag is normally not accessed directly by a program.

FIS Fast Interrupt Status Flag (FLAGS.1)

The FIS bit is set during a fast interrupt cycle and reset during the IRET following interrupt servicing. When set, it inhibits all interrupts and causes the fast interrupt return to be executed when the IRET instruction is executed.

BA Bank Address Flag (FLAGS.0)

The BA flag indicates which register bank in the set 1 area of the internal register file is currently selected, bank 0 or bank 1. The BA flag is cleared to "0" (select bank 0) when the SB0 instruction is executed and is set to "1" (select bank 1) when the SB1 instruction is executed.

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