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G2 PowerPC Core Reference Manual
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MOTOROLA
Signal Descriptions
8.3.7.1
Data Bus
The data bus consists of 64 input and 64 output signals on the G2 core. The data bus has
two halves—data bus high (dh) and data bus low (dl). See Table 8-10 for the data bus lane
assignments. The data bus is driven once for noncached transactions and four times for
cache transactions (bursts). The dh and dl signals are split into input, output, and input
enable signals on the G2 core.
8.3.7.1.1
Data Bus In (core_dh_in[0:31], core_dl_in[0:31])
Following are the state meaning and timing comments for core_dh_in[0:31] and
core_dl_in[0:31].
State Meaning
Asserted/Negated—Represents the state of data during a data read
transaction.
Timing Comments
Assertion/Negation—Data must be valid on the same bus clock
cycle that core_ta is asserted.
8.3.7.1.2
Data Bus Input Enable (core_dh_ien, core_dl_ien)—Output
core_dh_ien and core_dl_ien are input enable indicators to their corresponding bus signals.
Following are the state meaning and timing comments for core_dh_ien and core_dl_ien.
Note that not all input signals have input enable signals.
State Meaning
Asserted—Indicates that the G2 core is expecting valid data bus
input.
Negated—Indicates that the received data bus input is ignored.
Timing Comments
Assertion/Negation—Valid data must be present to data bus input
signals when core_dh_ien or core_dl_ien is asserted to the system
logic. These signals allow integrators to support either a bidirectional
or unidirectional data bus interface.
Table 8-10. Data Bus Lane Assignments
Data Bus
Signals
Byte Lane
dh[0:7]
0
dh[8:15]
1
dh[16:23]
2
dh[24:31]
3
dl[0:7]
4
dl[8:15]
5
dl[16:23]
6
dl[24:31]
7
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