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Long word

Figure 2.4 Data Format in Registers

2.2.2

Data Format in Memory

Memory data formats are classified into bytes, words, and long words. Byte data can be accessed

from any address, but an address error will occur if you try to access word data starting from an

address other than 2n or long word data starting from an address other than 4n. In such cases, the

data accessed cannot be guaranteed. The hardware stack area, which is referred to by the hardware

stack pointer (SP, R15), uses only long word data starting from address 4n because this area stores

the program counter and status register (figure 2.5).

Byte

Word

Long word

Address 2n

Address 4n

Address m

Address m + 2

Address m + 1

Address m + 3

Figure 2.5 Data Format in Memory

2.2.3

Immediate Data Format

Byte (8-bit) immediate data is located in the instruction code. Immediate data accessed by the

MOV, ADD, and CMP/EQ instructions is sign-extended and is handled in registers as long word

data. Immediate data accessed by the TST, AND, OR, and XOR instructions is zero-extended and

is handled as long word data. Consequently, AND instructions with immediate data always clear

the upper 24 bits of the destination register.

Word or long word immediate data is not located in the instruction code but rather is stored in a

memory table. The memory table is accessed by a immediate data transfer instruction (MOV)

using the PC relative addressing mode with displacement.

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