Data Units

The following data unit terminology is used throughout this manual.

Term

Words

Bytes

Bits

Other

 

 

 

 

 

Byte

½

1

8

Word

1

2

16

Longword

2

4

32

Dword

Quadword

4

8

64

2 longword

 

 

 

 

 

Do Not Care (X)

A capital X represents any valid value.

External

Unless otherwise stated, external means not contained in the chip.

Field Notation

The names of single-bit and multiple-bit fields can be used rather than the actual bit numbers (see Bit Notation). When the field name is used, it is contained in square brackets ([]). For example, RegisterName[LowByte] specifies RegisterName[7:0].

Note

Notes emphasize particularly important information.

Numbering

All numbers are decimal or hexadecimal unless otherwise indicated. The prefix 0x indi- cates a hexadecimal number. For example, 19 is decimal, but 0x19 and 0x19A are hexa- decimal (also see Addresses). Otherwise, the base is indicated by a subscript; for example, 1002 is a binary number.

Ranges and Extents

Ranges are specified by a pair of numbers separated by two periods (..) and are inclu- sive. For example, a range of integers 0..4 includes the integers 0, 1, 2, 3, and 4.

Extents are specified by a pair of numbers in square brackets ([]) separated by a colon

(:)and are inclusive. Bit fields are often specified as extents. For example, bits [7:3] specifies bits 7, 6, 5, 4, and 3.

Register Figures

The gray areas in register figures indicate reserved or unused bits and fields.

Bit ranges that are coupled with the field name specify the bits of the named field that are included in the register. The bit range may, but need not necessarily, correspond to the bit Extent in the register. See the explanation above Table 5–1for more information.

Signal Names

The following examples describe signal-name conventions used in this document.

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Compaq EV68A Data Units, Do Not Care, External, Field Notation, Numbering, Ranges and Extents, Register Figures