External Bus Interface
MOTOROLA
MPC801 USER’S MANUAL
13-7
13
NOTES:
O = Output from the MPC801.
I = Input to the MPC801.
TEA
1
Low
I
Transfer Error Acknowledge
current transaction was addressed to. It indicates that an error
condition has occurred during the bus cycle.
—Driven by the slave device the
O
Driven by the MPC801 when the internal bus monitor
erroneous bus condition.
detects an
BI
1
Low
I
Burst Inhibit
was addressed to. It indicates that the current slave does not
support burst mode.
—Driven by the slave device the current transaction
O
Driven by the MPC801 when the slave device is controlled by the
on-chip memory controller.
ARBITRATION
BR
1
Low
I
Bus Request
that an external master is requesting the bus.
—When the internal arbiter is asserted, it indicates
O
Driven by the MPC801 when the internal arbiter is disabled and
the chip is not parked
.
BG
1
Low
O
Bus Grant
asserts this signal to indicate that an external master can assume
ownership of the bus and begin a bus transaction. The BG signal
should be qualified by the master requesting the bus to ensure it
is the bus owner:
Qualified BG = BG & ~ BB
—When the internal arbiter is enabled, the MPC801
I
When the internal arbiter is disabled, the BG is sampled and
properly qualified by the MPC801 when an external bus
transaction is to be executed by the chip.
BB
1
Low
O
Bus Busy
asserts this signal to indicate that it is the current owner of the
bus. When the internal arbiter is disabled, it will assert this signal
after the external arbiter grants the chip ownership of the bus and
it is ready to start the transaction.
—When the internal arbiter is enabled, the MPC801
I
When the internal arbiter is enabled, the MPC801 samples this
signal to get an indication of when the external master ended its
bus tenure (BB negated).
When the internal arbiter is disabled, the BB is sampled to
properly qualify the BG signal when an external bus transaction
is to be executed by the chip.
Table 13-1. MPC801 System Interface Unit Signals (Continued)
MNEMONIC
PINS
ACTIVE
I/O
DESCRIPTION