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2
2.4 Accumulator
The accumulator (ACC) is a 56-bit register used by DSP function instructions. When read out or
written to, it is handled as a 64-bit register. When reading, the value of bit 8 is sign-extended. When
writing, bits 0--7 are ignored. Also, the accumulator is used by the multiplication instruction "MUL."
Note that when executing this instruction, the value of the accumulator is destroyed.
The "MVTACHI" and "MVTACLO" instructions are used to write to the accumulator. The
"MVTACHI" instruction writes data to the 32 high-order bits (bits 0-31), and the "MVTACLO"
instruction writes data to the 32 low-order bits (bits 32-63).
The "MVFACHI," "MVFACLO," and "MVFACMI" instructions are used to read data from the
accumulator. The "MVFACHI" instruction reads data from the 32 high-order bits (bits 0-31), the
"MVFACLO" instruction reads data from the 32 low-order bits (bits 32-63), and the "MVFACHI"
instruction reads data from the 32 middle bits (bits 16-47).
(Note)
0(MSB)
7 8
ACC
Range of bits read/written to by
MVFACHI/MVTACHI instructions
Note: Bits 0-7 always show the sign-extended value of bit 8. Writes to this bit field are ignored.
2.5 Program Counter
The Program Counter (PC) is a 32-bit counter used to hold the address of the currently executed
instruction. Because M32R instructions each start from an even address, the LSB (bit 31) is always
0.
0(MSB)
PC
Range of bits read by MVFACMI
instruction
15
16
31
PC
2-6
32
47
48
Range of bits read/written to by
MVFACLO/MVTACLO instructions
CPU
2.4 Accumulator
63(LSB)
31(LSB)
0
Ver.0.10
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