mcf5407 Freescale Semiconductor, Inc, mcf5407 Datasheet - Page 262

• Manufacturer Part Number: mcf5407
• Description: Mcf5407 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

Chip-Select Operation
10.3.1.1 8-, 16-, and 32-Bit Port Sizing
Static bus sizing is programmable through the port size bits, CSCR[PS]. See
Section 10.4.1.3, “Chip-Select Control Registers (CSCR0–CSCR7).” Figure 10-1 shows
the correspondence between data byte lanes and the external chip-select memory. Note that
all lanes are driven, although unused lines are undefined.
10.3.1.2 Global Chip-Select Operation
CS0, the global (boot) chip select, allows address decoding for boot ROM before system
initialization. Its operation differs from other external chip-select outputs after system reset.
After system reset, CS0 is asserted for every external access. No other chip-select can be
used until the valid bit, CSMR0[V], is set, at which point CS0 functions as configured and
CS[7:1] can be used. At reset, the port size, byte enable, and automatic acknowledge
functions of the global chip-select are determined by the logic levels of the inputs on
D[7:5,3]. Table 10-4 through Table 10-6 list the various reset encodings for the
configuration signals multiplexed with D[7:5,3].
10-4
Figure 10-1. Connections for External Memory Port Sizes
Table 10-4. D7/AA, Automatic Acknowledge of Boot CS0
32-bit port
16-bit port
8-bit port
data bus
External
memory
memory
memory
D7/AA
0
1
MCF5407 User’s Manual
D[31:24]
Byte 0
Byte 0
Byte 2
Byte 0
Byte 1
Byte 2
Byte 3
Disabled
Enable with 15 wait states
BE0
Boot CS0 AA Configuration at Reset
D[23:16]
Byte 1
Byte 1
Byte 3
BE1
Driven, undefined
D[15:8]
Byte 2
Driven, undefined
BE2
Byte 3
D[7:0]
BE3