
8-16
G2 PowerPC Core Reference Manual
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MOTOROLA
Signal Descriptions
Following are the state meaning and timing comments for core_a_out[0:31].
State Meaning
Asserted/Negated—Represents the physical address (real address)
of the data to be transferred. On burst transfers, the address bus out
signal presents the double-word-aligned address containing the
critical code or data that missed the cache on a read operation, or the
first double word of the cache line on a write operation. Note that the
address output during burst operations is not incremented. See
Section 9.3.2, “Address Transfer.”
Timing Comments
Assertion/Negation—Occurs on the bus clock cycle after a qualified
bus grant (coincides with assertion of core_abb_out and
core_ts_out).
High Impedance—Occurs one bus clock cycle after core_aack is
asserted, after the negation of core_a_oe, if core_a_tre is asserted. If
core_a_tre is negated, core_a_out[0:31] are always driven.
8.3.3.1.3
Address Bus Output Enable (core_a_oe)—Output
core_a_oe is an output-enable indicator to its corresponding bus signals. Following are the
state meaning and timing comments for core_a_oe.
State Meaning
Asserted—Indicates that the core is driving a valid
core_a_out[0:31].
Negated—Indicates one of the following two conditions:
If core_a_tre is negated, negated core_a_oe indicates that the core is
not driving valid core_a_out[0:31] values.
If core_a_tre is asserted, negated core_a_oe indicates that
core_a_out[0:31] are in the high-impedance state.
Timing Comments
Assertion/Negation—Occurs on the bus clock cycle after a qualified
bus grant (coincides with assertion of core_abb_out and
core_ts_out).
Note that negation of core_a_oe may force core_a_out[0:31] to the
high-impedance state, if core_a_tre is asserted.
8.3.3.1.4
Address Bus High-Impedance Enable (core_a_tre)—Input
Following are the state meaning and timing comments for core_a_tre. core_a_tre is a
high-impedance enable signal on the G2 core and can be used to create an external
bidirectional core_a_out[0:31] bus. When the related input/output signals (core_a_in[0:31]
and core_a_out[0:31]) are wire-ORed together, the resulting bus functions similar to a
bidirectional 60x address bus when core_a_tre is asserted. See Section 8.2.2.2, “Logic Gate
Equivalent and Bidirectional Signals,” for more information.
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