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2.2

Data Formats

2.2.1

Data Format in Registers

byte (8 bits) or a word (16 bits), it is sign-extended into a longword when loaded into a register.

Longword

Figure 2.6 Longword

2.2.2

Data Format in Memory

Memory data formats are classified into bytes, words, and longwords. Memory can be accessed in

8-bit byte, 16-bit word, or 32-bit longword form. A memory operand less than 32 bits in length is

sign-extended before being stored in a register.

A word operand must be accessed starting from a word boundary (even address of a 2-byte unit:

address 2n), and a longword operand starting from a longword boundary (even address of a 4-byte

unit: address 4n). An address error will result if this rule is not observed. A byte operand can be

accessed from any address.

Big-endian or little-endian byte order can be selected for the data format. The endian mode should

be set with the MD5 external pin in a power-on reset. Big-endian mode is selected when the MD5

pin is low, and little-endian when high. The endian mode cannot be changed dynamically. Bit

positions are numbered left to right from most-significant to least-significant. Thus, in a 32-bit

longword, the leftmost bit, bit 31, is the most significant bit and the rightmost bit, bit 0, is the least

significant bit.

The data format in memory is shown in figure 2.7. In little-endian mode, data written in byte-size

(8-bit) units should be read in byte-size units, and data written in word-size (16-bit) units should

be read in word-size units.

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