Chapter 2. Signal Descriptions and Clocking
2-11
Detailed Signal Descriptions
2.2.1.5.2 Command/Byte Enable (C/BE[3:0])—Input
Following is the state meaning for C/BE[3:0] as input signals.
State Meaning
Asserted/Negated—During the address phase, C/BE[3:0] indicate
the command that another master is sending. The MPC8240 uses the
value on these signals (in addition to the address) to determine
whether it is a target for a transaction. Table 2-3 summarizes the PCI
bus command encodings. See Section 7.3.3, “Addressing,” for more
information.
During the data phase, C/BE[3:0] indicate which byte lanes are valid.
2.2.1.6 Device Select (DEVSEL)
The device select (DEVSEL) signal is both an input and output on the MPC8240.
2.2.1.6.1 Device Select (DEVSEL)—Output
Following is the state meaning for DEVSEL as an output.
State Meaning
Asserted—Indicates that the MPC8240 has decoded the address of a
PCI transaction, and it is the target of the current access.
Negated—Indicates that the MPC8240 has decoded the address and
is not the target of the current access.
Table 2-3. PCI Command Encodings
C/BE[3:0]
PCI Command
0000
Interrupt acknowledge
0001
Special cycle
0010
I/O read
0011
I/O write
0100
Reserved
0101
Reserved
0110
Memory read
0111
Memory write
1000
Reserved
1001
Reserved
1010
Configuration read
1011
Configuration write
1100
Memory read multiple
1101
Dual address cycle
1
1
The MPC8240 does not generate this command or
the reserved commands.
1110
Memory read line
1111
Memory write and invalidate
Содержание MPC8240
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