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2-7

32182 Group User’s Manual (Rev.1.0)

CPU

2.4 Accumulator

The Accumulator (ACC) is a 56-bit register used for DSP function instructions.

The accumulator is handled as a 64-bit register when accessed for read or write. When reading data from the

accumulator, the value of bit 8 is sign-extended. When writing data to the accumulator, bits 0 to 7 are ignored. The

accumulator is also used for the multiply instruction “MUL,” in which case the accumulator value is destroyed by

instruction execution.

Use the MVTACHI and MVTACLO instructions for writing to the accumulator. The MVTACHI and MVTACLO

instructions write data to the high-order 32 bits (bits 0–31) and the low-order 32 bits (bits 32–63), respectively.

Use the MVFACHI, MVFACLO and MVFACMI instructions for reading data from the accumulator. The MVFACHI,

MVFACLO and MVFACMI instructions read data from the high-order 32 bits (bits 0–31), the low-order 32 bits (bits

32–63) and the middle 32 bits (bits 16–47), respectively.

After reset, the value of accumulator is undefined.

7 8

31 32

47 48

b63

ACC

(Note 1)

Read range of MVFACMI instruction

Write and read ranges of MVTACLO

and MVFACLO instructions

Write and read ranges of MVTACHI

and MVFACHI instructions

Note 1: When read, bits 0 to 7 always show the sign-extended value of the value of bit 8. Writing to this

bit field is ignored.

2.5 Program Counter

The Program Counter (PC) is a 32-bit counter that retains the address of the instruction being executed. Since the

M32R FPU instruction starts with even-numbered addresses, the LSB (bit 31) is always "0".

After reset, the value of PC is H’0000 0000.

b31

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