
Chapter 2. Signal Descriptions
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Chapter 2
Signal Descriptions
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This chapter describes the external signals used by the PowerPC 601, PowerPC 603, and
PowerPC 604 processors, identifying both the set of signals that are common to all 60x
processors as well as indicating characteristics of individual processor implementations. It
contains a concise description of individual signals, showing behavior when the signal is
asserted and negated and when the signal is an input and an output. Note that the
descriptions in this chapter are intended to provide a quick summary of signal functions.
Subsequent chapters describe the operation of many of these signals in greater detail, both
with respect to how individual signals function and how groups of signals interact.
NOTE
A bar over a signal name indicates that the signal is active low—for
example, ARTRY (address retry) and TS (transfer start). Active-low
signals are referred to as asserted (active) when they are low and
negated when they are high. Signals that are not active low, such as
AP[0–3] (address bus parity signals) and TT[0–4] (transfer type
signals) are referred to as asserted when they are high and negated
when they are low.
The clock, power, and test signals are not described in this document. Refer to the user’s
manual for the particular processor for this information.
The bus signal descriptions in this chapter are grouped by the categories shown in
Figure 1-2. The section names in this chapter correspond to those groups as defined in
Section 1.4, “Bus Interface Signals.” The sections describe state and timing descriptions for
each signal and indicate if a signal is an input or an output with respect to a PowerPC
processor. If a signal is both, the output characteristics are described first. The description
is from the perspective of the processor; no attempt is made to describe these signals as an
arbiter, slave, or target would see them.
The differences between how signals are implemented on different processors is
summarized in Section 2.12, “Summary of Signal Differences.”