
MOTOROLA
Chapter 8. Signal Descriptions
8-13
Signal Descriptions
8.3.1.3.2
Address Bus Busy Out (core_abb_out)
The core also implements address bus busy output enable and address bus busy
high-impedance enable signals. core_abb_out acts as follows:
If core_abb_tre is asserted, the output is in one of the following three states—high
impedance, driven high, or driven low.
If core_abb_tre is negated, the output is either driven to the high or low state. In this
case, a valid value on core_abb_out exists when core_abb_oe is asserted.
Following are the state meaning and timing comments for core_abb_out.
State Meaning
Asserted—Indicates that the core is the 60x address bus master. See
Section 9.3.1, “Address Bus Arbitration.”
Negated—Indicates that the core is not using the address bus. If
core_abb_out is negated during the bus clock cycle following a
qualified bus grant, the core does not accept mastership, even if
core_br is asserted. This can occur if a potential transaction is
aborted internally before the transaction is started.
Timing Comments
Assertion—Occurs on the bus clock cycle following a qualified
core_bg that is accepted by the processor.
Negation—Occurs for a minimum of one-half bus clock cycle
following the assertion of core_aack. If core_abb_out is negated
during the bus clock cycle following a qualified bus grant, the core
does not accept mastership, even if core_br is asserted.
High Impedance—Occurs one-half clock cycle after core_abb_out is
negated, after the negation of core_abb_oe, if core_abb_tre is
asserted. If core_abb_tre is negated, core-abb_out is always driven.
8.3.1.3.3
Address Bus Busy Output Enable (core_abb_oe)—Output
core_abb_oe is an output-enable indicator to its corresponding bus signals. Following are
the state meaning and timing comments for core_abb_oe.
State Meaning
Asserted—Indicates that the core is driving a valid core_abb_out.
Negation—Indicates one of the following two conditions:
If core_abb_tre is negated, negated core_abb_oe indicates that the
core is not driving a valid core_abb_out value.
If core_abb_tre is asserted, negated core_abb_oe indicates that
core_abb_out is in the high-impedance state.
Timing Comments
Assertion—Occurs one clock cycle after an accepted qualified bus
grant and remains asserted for the duration of the address tenure.
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