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G2 PowerPC Core Reference Manual
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MOTOROLA
Signal Descriptions
State Meaning
Asserted—Indicates that the G2 core may, with the proper
qualification, assume mastership of the 60x address bus. See
Section 9.3.1, “Address Bus Arbitration.”
Negated—Indicates that the core is not the next potential address bus
master.
Assertion—May occur at any time to indicate the core is free to use
the address bus. After the core assumes bus mastership, it does not
check for a qualified bus grant again until the cycle during which the
address bus tenure is completed (assuming it has another transaction
to run). The core does not accept a core_bg in the cycles between the
assertion of either core_ts_in or core_ts_out and core_aack.
Negation—May occur anytime to indicate the core cannot use the
bus. The core may still assume bus mastership on the bus clock cycle
of the negation of core_bg because during the previous cycle
core_bg indicated to the core that it was free to take mastership (if
qualified).
Timing Comments
8.3.1.3
Address Bus Busy
There is both an address bus busy input and address bus busy output signal on the G2 core.
The core also implements address bus busy output enable and address bus busy
high-impedance enable signals.
8.3.1.3.1
Address Bus Busy In (core_abb_in)
Following are the state meaning and timing comments for core_abb_in.
State Meaning
Asserted—Indicates that the address bus is in use. This condition
effectively blocks the core from assuming address bus ownership,
regardless of the core_bg input; see Section 9.3.1, “Address Bus
Arbitration.”
Negated—Indicates that the address bus is not owned by another bus
master and that it is available to the core when accompanied by a
qualified bus grant.
Timing Comments
Assertion—May occur when the core must be prevented from using
the address bus (and the processor is not currently asserting
core_abb_out).
Negation—May occur whenever the core can use the address bus.
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