Registers
14.1.4
Register Attribute Definition
Table 14-2. Register Attributes Definitions
Attribute
Read Only
Abbreviation
RO
Description
This bit is set by the hardware. Software can only read the bit. Writes to
the register have no effect.
Write Only
Read/Write
WO
The bit is not implemented as a bit. The write causes some hardware
event to take place. Read returns all zeroes.
RW
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 RRW
Write
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
The bit is “sticky” or unchanged by a link reset. These bits can only be
defaulted by a power-up reset.
with “ST”
appended to the
end
Reserved
RV
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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Intel® 6400/6402 Advanced Memory Buffer Datasheet
INTEL [ INTEL ]
