VR4102 datasheet(47/701 Pages) NEC

47 / 701 page

CHAPTER 1 INTRODUCTION

1.5.4 Data Formats and Addressing

The VR4102 uses following four data formats:

Doubleword (64 bits)

Word (32 bits)

Halfword (16 bits)

Byte (8 bits)

For the VR4100 CPU core, byte ordering within all of the larger data formats - halfword, word, doubleword - can

be configured in either big-endian or little-endian order. However, the VR4102 supports the little-endian order

only.

Endianness refers to the location of byte 0 within the multi-byte data structure. Figure 1-5 shows the ordering of

bytes within words and the ordering of words within doubleword structures for the little-endian conventions.

When configured as a little-endian system, byte 0 is always the least-significant (rightmost) byte, which is

compatible with iAPXTM and DEC VAXTM conventions. Figure 1-5 shows this configuration.

Figure 1-5. Little-Endian Byte Ordering in Word Data

Lower

address

Higher

address

Word

address

Bit No.

Remarks 1. The lowest byte is the lowest address.

2. The address of word data is specified by the lowest byte’s address.

In this manual, bit 0 is always the least-significant (rightmost) bit; thus, bit designations are always little-endian.

Figure 1-6 shows little-endian byte ordering in doublewords.

VR4102 Datasheet(PDF) 47 Page - NEC