MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor
16-7
This allows a code, written to run from internal flash memory, to be executed from the external memory.
16.3.2.2.2
Single Bus Master or Multiple Bus Masters
External boot mode has two options for booting:
•
External boot with no arbitration — This option is a single master system where the MCU is the
only bus master in the system and therefore does not need to consider arbitration of the external
bus.
•
External boot with external arbitration — This option is where there is another bus master on the
external bus and arbitration of the bus is handled external to the MCU.
These two modes are selected based on the state of the two BOOTCFG pins.
In a multiple master system where both are booting from the same external bus memory, one boots in
external boot with no arbitration mode while the other boots in external boot with external arbitration
mode.
The configuration of the EBI is different for the two modes.
16.3.2.2.3
External Boot—Single Master with no Arbitration EBI Configuration
The BAM program configures:
1. Chip select CS0 region as a 16-bit port with a base address of 0x2000_0000, no burst, 15 wait
states, 8 MB size.
2. EBI for no external master (clear EXTM bit).
3. Enables the EBI for normal operation.
4. Configures the following I/O pins as bus signals: address signals[8:31]; data[0:15]; WE0; OE;
TS; CS0. Data[16:31] is also configured if RCHW[PS0] = 0.
16.3.2.2.4
External Boot with External Arbitration EBI Configuration
In the external boot mode with external arbitration the BAM program also does the following:
1. Sets the EXTM bit, enabling the EBI for external master operation.
2. Configures EBI for external arbitration (sets the EARB bit).
3. Configures the additional I/O signals BB, BG, BR for bus function. (This applies only to the
Table 16-5. MMU Configuration for an External Boot
TLB
Entry
Region
Logical Base
Address
Physical Base
Address
Size
Attributes
1
Internal flash
memory
0x0000_0000
0x2000_0000
16 MB
• Cache enabled
• Not guarded
• Big Endian
• Global PID
2
EBI
0x2000_0000
0x2000_0000
16 MB
• Cache enabled
• Not guarded
• Big Endian
• Global PID
Summary of Contents for MPC5553
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