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MPC563XM Reference Manual, Rev. 1
Freescale Semiconductor
373
Preliminary—Subject to Change Without Notice
To operate two masters in External Master Mode, one must be configured for internal arbitration and the
other must be configured for external arbitration. Connecting three or more masters together in the same
system is not supported by this EBI.
Most of the bidirectional signals shown in
are only driven by the EBI when the EBI owns the
external bus. The only exceptions are the TA and TEA signals (described in
Section 13.5.2.9, “Termination
) and the DATA bus, which are driven by the EBI for external master reads to internal
address space. As long as the external master device follows the same protocol for driving signals as this
EBI, there is no need to use the open drain mode of the pads configuration module for any EBI pins.
The PowerPC Storage Reservation protocol is not supported by the EBI. Coherency between multiple
masters must be maintained via software techniques, such as event passing.
The EBI does not provide memory controller services to an external master that accesses shared external
memories. Each master must properly configure its own memory controller and drive its own chip selects
when sharing a memory between two masters.
The EBI does not support burst accesses from an external master; only single accesses of 8, 16, or 32 bits
can be performed.
1
While the EBI (master) supports up to a 29-bit address bus for internal master accesses, only 24 bits
(ADDR[8:31]) are used by the EBI (slave) for external master accesses. The values on ADDR[3:7] are
ignored.
13.5.2.10.1
Address Decoding for External Accesses
The external address is compared for any external master access, in order to determine if EBI operation is
required. Since <32 address bits are available on the external bus, special decoding logic is required to
allow an external master to access on-chip locations whose upper 8 address bits are non-zero. This is done
by using ADDR[8:11] (the upper 4 bits of 24-bit address bus that is used for external master accesses) as
a code to determine whether the access is on-chip and if so, which internal slave it is targeted for.
Below is the address compare sequence:
•
External master access to another device - If ADDR[8]=0, then the access is assumed to be to
another device and is ignored by the EBI.
•
External master access to valid internal slave - If ADDR[8]=1, then ADDR[9:11] are checked
versus a list of 3-bit codes (MCU-specific) to determine which internal slave to forward the access
to. The upper 8 internal address bits are set appropriately by the EBI according to this 3-bit code,
and internal address bits [8:11] are also set appropriately to match the internal slave selected.
•
External master access to invalid internal slave - If the 3-bit code does not match a valid internal
slave, the EBI sets internal address bits [0:11] to an "invalid slave" code and the internal bridge is
required to properly respond with bus error so that the system does not hang.
Refer to the device-specific SoC Guide to see the translation codes and addresses used for a particular
MCU.
Section 13.6.5, “Address Decoding Example for External Master Accesses
1.
Except for the special case of a 32-bit non-chip-select access in 16-bit data bus mode. See
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