HD6417660 RENESAS [Renesas Technology Corp], HD6417660 Datasheet - Page 83

• Manufacturer Part Number: HD6417660
• Description: Renesas 32-Bit RISC Microcomputer
• Manufacturer: RENESAS [Renesas Technology Corp]

2.4
2.4.1
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.
2.4.2
Memory data formats are classified into byte, word, and longword. Memory can be accessed in
bytes, words, and longwords. 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.
Word operand must be accessed from word boundary (even address in two bytes: address 2n) and
longword operand must be accessed from longword boundary (even address in four bytes: address
4n). Otherwise, an address error will occur and an exception handling state will be entered. Byte
operand can be accessed from any address.
When a word or longword operand is accessed, the byte positions on the memory corresponding to
the word or longword data on the register is determined according to the specified endian mode
(big endian or little endian).
Figure 2.10 shows a byte correspondence in big endian mode. In big endian mode, the MSB byte
in the register corresponds to the lowest address in the memory, and the LSB byte in the register
corresponds to the highest address. For example, if the contents of the general register R0 is
stored at an address indicated by the general register R1 in longwords, the MSB byte in R0 is
stored at the address indicated by the R1 and the LSB byte in R0 is stored at the address indicated
by the (R1 + 3).
The on-chip device registers assigned to memory are accessed in big endian mode. Note that the
available access size (byte, word, or longword) differs in each register.
Note: The CPU instruction codes of this LSI must be stored in words. In big endian mode, the
instruction code must be stored from upper byte to lower byte in this order from the word
boundary on the memory.
Data Formats
Register Data Format
Memory Data Formats
31
Longword
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