Specifications

17 January 1997 – Subject to Change

In some cases, more than one schematic page is referenced. For example, the

following specifies schematic pages 10 through 13:

“. . . the data switches (

pc164.10–13

) . . .”

Signal Names

All signal names are printed in boldface type. Signals whose name originates in an

industry-standard specification, such as PCI or IDE, are printed in the case as found

in the specification (usually uppercase). Active-high signals are indicated by the

suffix. Active-low signals have the

suffix, a pound sign “#” appended, or a “not”

overscore bar. Signals with no suffix are considered high-asserted signals. For

example, signals

data_h<127:0>

and

cia_int

are active-high signals. Signals

mem_ack_l

FRAME#

, and

RESET

are active-low signals.

UNPREDICTABLE and UNDEFINED

Throughout this manual the terms UNPREDICTABLE and UNDEFINED are used.

Their meanings are quite different and must be carefully distinguished.

In particular, only privileged software (that is, software running in kernel mode) can

trigger UNDEFINED operations. Unprivileged software cannot trigger

UNDEFINED operations. However, either privileged or unprivileged software can

trigger UNPREDICTABLE results or occurrences.

UNPREDICTABLE results or occurrences do not disrupt the basic operation of the

processor. The processor continues to execute instructions in its normal manner. In

contrast, UNDEFINED operations can halt the processor or cause it to lose

information.

The terms UNPREDICTABLE and UNDEFINED can be further described as

follows:

•

UNPREDICTABLE

– Results or occurrences specified as UNPREDICTABLE might vary from

moment to moment, implementation to implementation, and instruction to

instruction within implementations. Software can never depend on results

specified as UNPREDICTABLE.

– An UNPREDICTABLE result might acquire an arbitrary value that is

subject to a few constraints. Such a result might be an arbitrary function of

the input operands or of any state information that is accessible to the

process in its current access mode. UNPREDICTABLE results may be

unchanged from their previous values.