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MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor
12-5
mode are modes that the MCU may enter, in parallel to the EBI being configured in one of its
module-specific modes.
12.1.4.1
Single Master Mode
In single master mode, the EBI responds to internal requests matching one of its regions, but ignores all
externally-initiated bus requests. The MCU is the only master allowed to initiate transactions on the
external bus in this mode; therefore, it acts as a parked master and does not have to arbitrate for the bus
before starting each cycle. The BR, BG, and BB signals are not used by the EBI in this mode, and are
available for use in an alternate function by another module of the MCU. Single master mode is entered
when EXTM = 0 and MDIS = 0 in the EBI_MCR.
NOTE
On the MPC5553, the arbitration pins (BB, BR, BG) are not functional.
12.1.4.2
External Master Mode
When the MCU is in external master mode, the EBI responds to internal requests matching one of its
regions, and also to external master accesses to internal address space. In this mode, the BR, BG, and BB
signals are all used by the EBI to handle arbitration between the MCU and an external master. External
master mode is entered when EXTM = 1 and MDIS = 0 in the EBI_MCR register.
Because in the MPC5553 the arbitration pins (BB, BR, BG) are not functional, dual-master operation
(multiple masters initiating external bus cycles) is not supported. However, a multi-MCU system with one
master and one slave is supported. In such a dual-controller system, if the EBI is configured to internal
arbitration (EARB=0 in EBI_MCR), it must be used as the system master. If configured to external
arbitration (EARB=1 in EBI_MCR), it must be the system slave.
NOTE
In the MPC5553, the internal bus grant input of the EBI is tied to a negated
state. In a dual controller system in which the EBI is programmed to
External Master Mode with external arbitration, if the CPU tries to access a
memory region within the EBI space, it will never get a bus grant, and the
operation will time out.
Because the MPC5553 does not have transfer size pins (TSIZ[0:1]), the SIZEN and SIZE fields of the
EBI_MCR must be used for MCU-to-MCU transfers to indicate transfer size.
Section 12.5.5, “Dual-MCU Operation with Reduced Pinout MCUs
.”
External master mode operation is described in
Section 12.4.2.10, “Bus Operation in External Master
12.1.4.3
Module Disable Mode
The module disable mode is used for MCU power management. The clock to the non-memory mapped
logic in the EBI is stopped while in module disable mode. Requests (other than to memory-mapped logic)
must not be made to the EBI while it is in module disable mode, even if the clocks have not yet been shut
off. In this case, the behavior is undefined. Module disable mode is entered when MDIS = 1 in the
EBI_MCR.
Содержание MPC5553
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