Freescale Semiconductor MPC5553, Reference Manual

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MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
12-8 Freescale Semiconductor
12.2.1.2 Bus Busy (BB) — MPC5554 Only
BB is asserted to indicate that the current bus master is using the bus. The BB signal is only used by the
EBI when the EBI is in external master mode. In single master mode, the BB signal is never asserted or
sampled by the EBI.
When configured for internal arbitration, the EBI asserts BB to indicate that it is currently using the bus.
An external master must not begin a transfer until this signal is negated for two cycles. The EBI does not
negate this signal until its transfer is complete. When not driving BB, the EBI samples this signal to get an
indication of when the external master is no longer using the bus (BB negated for two cycles).
When configured for external arbitration, the EBI asserts this signal when it is ready to start the transaction
after the external arbiter has granted ownership of the bus to the MCU. When not driving BB, the EBI
samples this signal to properly qualify the BG line when an external bus transaction is to be executed by
the MCU.
12.2.1.3 Burst Data in Progress (BDIP)
BDIP is asserted to indicate that the master is requesting another data beat following the current one.
BDIP is driven by the EBI or an external master depending on who owns the external bus. This signal is
driven by the EBI on all EBI-mastered external burst cycles, but is only sampled by burst mode memories
that have a corresponding pin. See
Section 12.4.2.5, “Burst Transfer .”
12.2.1.4 Bus Grant (BG) — MPC5554 Only
BG is asserted to grant ownership of the external bus to the requesting master. The BG signal is only used
by the EBI when the EBI is in external master mode. In single master mode, the BG signal is never asserted
or sampled by the EBI.
When configured for internal arbitration, BG is output only and is asserted by the EBI to indicate that an
external master may assume ownership of the bus. The BG signal should be qualified by the master
requesting the bus in order to ensure it is the bus owner before beginning a bus transaction: Qualified bus
grant = BG and ~BB. The EBI negates BG following the negation of BR if it has an internal request for
the external bus pending. Otherwise, it keeps BG asserted to park the bus for the external master. The
parked external master could then assert BB to run subsequent transactions without the normal
requirement to assert BR.
When configured for external arbitration, BG is input only and is sampled and qualified (Qualified BG = ~
BB and BG) by the EBI when an external bus transaction is to be executed by the MCU.
NOTE
The MPC5553 does not implement BG, thus for this device the ball’s
primary function is the calibration address CAL_ADDR[11].
12.2.1.5 Bus Request (BR) — MPC5554 Only
BR is asserted to request ownership of the external bus. The BR signal is only used by the EBI when the
EBI is in external master mode. In single master mode, the BR signal is never asserted or sampled by the
EBI.
When configured for internal arbitration, BR is input only and is asserted by an external master when it is
requesting the bus.