
Chapter 2. Signal Descriptions
2-7
2.3.4 Address Bus (A[0–31])—Input (Direct-Store Operations)
Following are state and timing descriptions for A[0–31] as input signals for direct-store
operations.
State Meaning
Asserted/Negated—When the processor receiving A[0–31] signals is
not the master, it snoops (and checks address parity) on only the first
address beat of all direct-store operations for I/O reply operations
whose receiver tags match the processor identification (PID) tag. See
Section 7.1, “Direct-Store Transaction Protocol Details.”
Timing Comments
Assertion/Negation—The first beat of the I/O transfer address tenure
coincides with XATS, with the second address beat on the next cycle.
2.3.5 Address Bus Parity (AP[0–3])—Output
Following are state and timing descriptions for the address bus parity signals (AP[0–3]) as
output signals.
State Meaning
Asserted/Negated—Represents one bit of odd parity for each of four
address bus bytes. Odd parity means an odd number of bits,
including the parity bit, are driven high. Signal assignments are as
follows:
AP0
A[0–7]
AP1
A[8–15]
AP2
A[16–23]
AP3
A[24–31]
For more information, see Section 3.2.2.1, “Address Bus Parity.”
Timing Comments
Assertion/Negation/High Impedance—The same as A[0–31].
2.3.6 Address Bus Parity (AP[0–3])—Input
Following are state and timing descriptions for AP[0–3] as input signals.
State Meaning
Asserted/Negated—Represents one bit of odd parity for each of four
address bus bytes for snooping and direct-store operations.
Depending on MSR[ME] and various HID0 bits, detecting even
parity either causes the processor to enter the checkstop state or take
a machine check exception. If address parity check is enabled in
HID0, detection of even parity unconditionally causes a checkstop in
the 601. (See the APE signal description.)
Timing Comments
Assertion/Negation—The same as A[0–31].