Renesas SH7041 Series, Руководство по оборудованию, Страница: 86 / 923

48
2.2 Data Formats
2.2.1 Data Format in Registers
Register operands are always longwords (32 bits). When the memory operand is only a byte (8
bits) or a word (16 bits), it is sign-extended into a longword when loaded into a register (figure
2.4).
31 0
Longword
Figure 2.4 Longword Operand
2.2.2 Data Format in Memory
Memory data formats are classified into bytes, words, and longwords. 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 longword data starting from an address other than 4n. In such cases, the
data accessed cannot be guaranteed. The hardware stack area, referred to by the hardware stack
pointer (SP, R15), uses only longword data starting from address 4n because this area holds the
program counter and status register (figure 2.5).
31 0 15 23 7
Byte Byte Byte Byte
Word Word Address 2n
Address 4n Longword
Address m Address m + 2
Address m + 1 Address m + 3
Figure 2.5 Byte, Word, and Longword Alignment
2.2.3 Immediate Data Format
Byte (8-bit) immediate data resides in an instruction code. Immediate data accessed by the MOV,
ADD, and CMP/EQ instructions is sign-extended and handled in registers as longword data.
Immediate data accessed by the TST, AND, OR, and XOR instructions is zero-extended and
handled as longword data. Consequently, AND instructions with immediate data always clear the
upper 24-bits of the destination register.