
MOTOROLA
Chapter 2. Signal Descriptions
2-33
Timing Comments
Assertion—SDRAS is valid on the rising edge of the 60x bus clock
when a CS
n
signal is asserted.
2.2.4.22 Write Enable (WE)—Output
The write enable (WE) signal is an output on the MPC106. Following are the state meaning
and timing comments for the WE output signal.
State Meaning
Asserted—Enables writing to DRAM, EDO, or Flash.
–or–
For SDRAM, WE is part of the SDRAM command encoding. See
Section 6.4, “SDRAM Interface Operation,” for more information.
Negated—No DRAM, EDO, or Flash write operation is pending.
Timing Comments
Assertion—For DRAM, the MPC106 asserts WE concurrent with
the column address and prior to CAS
n
. For SDRAM, the MPC106
asserts WE concurrent with SDCAS for write operations.
2.2.5 PCI Interface Signals
This section provides descriptions of the PCI interface signals on the MPC106. Note that
throughout this manual, signals and bits of the PCI interface are referenced in little-endian
format.
2.2.5.1 PCI Address/Data Bus (AD[31–0])
The PCI address/data bus (AD[31–0]) consists of 32 signals that are both input and output
signals on the MPC106.
2.2.5.1.1 Address/Data (AD[31–0])—Output
Following is the state meaning for AD[31–0] as output signals.
State Meaning
Asserted/Negated—Represents the physical address during the
address phase of a PCI transaction. During the data phase(s) of a PCI
transaction, AD[31–0] contain data being written.
The AD[7–0] signals define the least-significant byte and AD[31–24]
the most-significant byte.
2.2.5.1.2 Address/Data (AD[31–0])—Input
Following is the state meaning for AD[31–0] as input signals.
State Meaning
Asserted/Negated—Represents the address to be decoded as a check
for device select during the address phase of a PCI transaction or data
being received during the data phase(s) of a PCI transaction.
2.2.5.2 Command/Byte Enable (C/BE[3–0])
The four command/byte enable (C/BE[3–0]) signals are both input and output signals on
the MPC106.