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M38509FEH-XXXSP Datasheet(PDF) 9 Page - Renesas Technology Corp |
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M38509FEH-XXXSP Datasheet(HTML) 9 Page - Renesas Technology Corp |
9 / 88 page Rev.2.10 2005.11.14 page 9 of 86 REJ03B0093-0210 3850 Group (Spec.A) •Bit 4: Break flag (B) The B flag is used to indicate that the current interrupt was generated by the BRK instruction. The BRK flag in the processor status register is always “0”. When the BRK instruction is used to generate an interrupt, the processor status register is pushed onto the stack with the break flag set to “1”. •Bit 5: Index X mode flag (T) When the T flag is “0”, arithmetic operations are performed between accumulator and memory. When the T flag is “1”, direct arithmetic operations and direct data transfers are enabled between memory locations. •Bit 6: Overflow flag (V) The V flag is used during the addition or subtraction of one byte of signed data. It is set if the result exceeds +127 to -128. When the BIT instruction is executed, bit 6 of the memory location operated on by the BIT instruction is stored in the overflow flag. •Bit 7: Negative flag (N) The N flag is set if the result of an arithmetic operation or data transfer is negative. When the BIT instruction is executed, bit 7 of the memory location operated on by the BIT instruction is stored in the negative flag. Table 5 Set and clear instructions of each bit of processor status register Set instruction Clear instruction C flag Z flag I flag D flag B flag T flag V flag N flag SEC CLC _ _ SEI CLI SED CLD _ _ SET CLT CLV _ _ _ [Processor status register (PS)] The processor status register is an 8-bit register consisting of 5 flags which indicate the status of the processor after an arithmetic operation and 3 flags which decide MCU operation. Branch opera- tions can be performed by testing the Carry (C) flag , Zero (Z) flag, Overflow (V) flag, or the Negative (N) flag. In decimal mode, the Z, V, N flags are not valid. •Bit 0: Carry flag (C) The C flag contains a carry or borrow generated by the arithmetic logic unit (ALU) immediately after an arithmetic operation. It can also be changed by a shift or rotate instruction. •Bit 1: Zero flag (Z) The Z flag is set if the result of an immediate arithmetic operation or a data transfer is “0”, and cleared if the result is anything other than “0”. •Bit 2: Interrupt disable flag (I) The I flag disables all interrupts except for the interrupt generated by the BRK instruction. Interrupts are disabled when the I flag is “1”. •Bit 3: Decimal mode flag (D) The D flag determines whether additions and subtractions are executed in binary or decimal. Binary arithmetic is executed when this flag is “0”; decimal arithmetic is executed when it is “1”. Decimal correction is automatic in decimal mode. Only the ADC and SBC instructions can be used for decimal arithmetic. |
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