6402 datasheet(160/250 Pages) INTEL

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Registers

160

Intel® 6400/6402 Advanced Memory Buffer Datasheet

14.1.4

Table 14-2. Register Attributes Definitions

Attribute

Abbreviation

Description

Read Only

This bit is set by the hardware. Software can only read the bit. Writes to

the register have no effect.

Write Only

The bit is not implemented as a bit. The write causes some hardware

event to take place. Read returns all zeroes.

Read/Write

The bit can be read or written by software.

Read/Write /

Clear

RWC

The bit can be either read or cleared by software. In order to clear a bit,

the software must write a one to it. Writing a zero to an RWC bit will have

no effect. Hardware will set this bit.

Read/Write /

Set

RWS

The bit can be either read or set by software. In order to set this RWS bit,

the software must write a one to it. Writing a zero to an RWS bit will have

no effect. Hardware will clear this bit.

Read/Write

Lock

RWL

The bit can be read and written by software. Hardware or a configuration

bit can lock this bit and prevent it from being updated.

Read/Write

Once

RWO

The bit can be read by software. It can also be written by software but the

hardware prevents writing/setting it more than once without a prior

“effective” reset. This protection applies on a byte-by-byte basis. For

example, if a two-bit RWO field straddles a byte boundary and only one

byte is written, then the written bit cannot be rewritten (unless reset).

However, the unwritten bit can still be written once. This is a special form

of RWL

Read/Restricted

Write

RRW

The bit field can be read by software. Only a restricted set of values can

be written through a configuration write in-band from the host. Illegal

values will be aborted and dropped.

Sticky

All of the above

with “ST”

appended to the

end

The bit is “sticky” or unchanged by a link reset. These bits can only be

defaulted by a power-up reset.

Reserved

This bit is reserved for future expansion and must not be written. The PCI

Local Bus Specification, Revision 2.2 requires that reserved bits must be

preserved. Any software that modifies a register that contains a reserved

bit is responsible for reading the register, modifying the desired bits, and

writing back the result.

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