Compaq EV67, 21264 specifications W1C, W1S, Addresses, Aligned and Unaligned, Bit Notation

Abbreviation	Meaning
RW	Read/Write
	Bits and fields can be read and written.
RW,n	Read/Write, and takes the value n at power-on reset.
	Bits and fields can be read and written.
W1C	Write One to Clear
	If read operations are allowed to the register, then the value may be read by
	software. If it is a write-only register, then a read operation by software
	returns an UNPREDICTABLE result. Software write operations of a 1 cause
	the bit to be cleared by hardware. Software write operations of a 0 do not
	modify the state of the bit.
W1S	Write One to Set
	If read operations are allowed to the register, then the value may be read by
	software. If it is a write-only register, then a read operation by software
	returns an UNPREDICTABLE result. Software write operations of a 1 cause
	the bit to be set by hardware. Software write operations of a 0 do not modify
	the state of the bit.
WO	Write Only
	Bits and fields can be written but not read.
WO,n	Write Only, and takes the value n at power-on reset.
	Bits and fields can be written but not read.

•Sign extension

SEXT(x) means x is sign-extended to the required size.

Addresses

Unless otherwise noted, all addresses and offsets are hexadecimal.

Aligned and Unaligned

The terms aligned and naturally aligned are interchangeable and refer to data objects that are powers of two in size. An aligned datum of size 2n is stored in memory at a byte address that is a multiple of 2n; that is, one that has n low-order zeros. For ex- ample, an aligned 64-byte stack frame has a memory address that is a multiple of 64.

A datum of size 2n is unaligned if it is stored in a byte address that is not a multiple of 2n.

Bit Notation

Multiple-bit fields can include contiguous and noncontiguous bits contained in square brackets ([]). Multiple contiguous bits are indicated by a pair of numbers separated by a colon [:]. For example, [9:7,5,2:0] specifies bits 9,8,7,5,2,1, and 0. Similarly, single bits are frequently indicated with square brackets. For example, [27] specifies bit 27. See also Field Notation.

Caution

Cautions indicate potential damage to equipment or loss of data.

xx Alpha 21264/EV67 Hardware Reference Manual