External Bus Interface
13-4
MPC801 USER’S MANUAL
MOTOROLA
13
13.3 SIGNAL DESCRIPTIONS
The following table describes each bus interface signal. More detailed descriptions of these
signals can be found in subsequent sections of this manual.
.
Table 13-1. MPC801 System Interface Unit Signals
MNEMONIC
PINS
ACTIVE
I/O
DESCRIPTION
ADDRESS AND TRANSFER ATTRIBUTES
A[6:31]
32
High
O
Address Bus
bus. It specifies the physical address of the bus transaction.
These signals can change during a transaction when controlled
by the memory controller.
—Driven by the MPC801 when it owns the external
I
Used only for testing purposes. Sampled by the MPC801 when
the external master initiates a transaction and the memory
controller is configured to handle external masters.
RD/WR
1
High
O
Read/Write
when it owns the external bus. Driven high indicates that a read
access is in progress and driven low indicates that a write access
is in progress.
—Driven by the MPC801 along with the address
I
Used only for testing purposes. Sampled by the MPC801 when
the external master initiates a transaction and the memory
controller is configured to handle external masters.
BURST
1
High
O
Burst Transfer
when it “owns” the external bus. Driven low indicates that a burst
transfer is in progress and driven high indicates that the current
transfer is not a burst.
—Driven by the MPC801 along with the address
I
Used only for testing purposes. Sampled by the MPC801 when
the external master initiates a transaction and the memory
controller is configured to handle external masters.
TSIZ[0:1]
2
High
O
Transfer Size
when it owns the external bus. It specifies the data transfer size
for the transaction.
—Driven by the MPC801 along with the address
I
Used only for testing purposes. Sampled by the MPC801 when
the external master initiates a transaction and the memory
controller is configured to handle external masters.
AT[0:3]
3
High
O
Address Type
when it owns the external bus. It provides additional information
about the address on the current transaction.
—Driven by the MPC801 along with the address
I
Used only for testing purposes.
RSV
1
High
O
Reservation Transfer
address when it owns the external bus. It provides additional
information about the address on the current transaction.
—Driven by the MPC801 along with the
I
Used only for testing purposes.