MMC2001
INTEGER CPU
MOTOROLA
REFERENCE MANUAL
2-11
2.8.4 Bus Operation
The following sections provide a functional description of the system bus, the signals
that control it, and the bus cycles provided for data transfer operations. They also
describe the error conditions and reset operation.
Table 2-2 M•CORE Bus Signals
Signal Name
Pins
Active
I/O
Description
Address and Transfer Attributes
ADDR[31:0]
Address Bus
32
High
O
Driven by the M•CORE to specify the physical address of
the bus transaction.
R/W
Read/Write
1
High
O
Driven by the M•CORE along with the address. Driven
high indicates that a read access is in progress. Driven
low indicates that a write access is in progress.
TSIZ[1:0]
Transfer Size
2
High
O
Driven by the M•CORE along with the address. Specifies
the data transfer size for the transaction.
TC[2:0]
Transfer Code
3
High
O
Driven by the M•CORE along with the address. Indicates
the type of access for the current bus cycle.
Transfer Request/Transfer Busy
TREQ
Transfer Request
1
Low
O
Driven by the M•CORE along with the address and trans-
fer attributes to indicate that a new access has been
requested.
TBUSY
Transfer Busy
1
Low
O
Driven by the M•CORE to indicate that an access is in
progress. This signal is driven for the duration of a cycle
and may be held asserted for multiple transfers.
Data
DATA[31:0]
Data Bus
32
High
O
Driven by the M•CORE when it “owns” the bus and it initi-
ated a write transaction to a slave device. Eight (byte), 16
(halfword), or 32 (word) bits of data can be transferred
per access.
I
Driven by the slave in a read transaction. Eight (byte), 16
(halfword), or 32 (word) bits of data can be transferred
per access.
Transfer Cycle Termination and Status
TA
Transfer Acknowledge
1
Low
I
Driven by the slave device to which the current transac-
tion was addressed. Indicates that the slave has received
the data on the write cycle or returned data on the read
cycle.
TEA
Transfer Error
Acknowledge
1
Low
I
Driven by the slave device to which the current transac-
tion was addressed. Indicates that an error condition has
occurred during the bus cycle.
ABORT
Abort
1
Low
O
Driven by the M•CORE to indicate that the transfer is to
be aborted immediately.
Power Management
LPMD[1:0]
Low-Power Modes
2
Low
O
Driven by the M•CORE to indicate whether the core is
running in normal mode or has just executed a low power
mode instruction.
Debug
DBGACK
Debug Mode
1
Low
O
Driven by the M•CORE to indicate that debug mode has
been entered.
Freescale Semiconductor,
I
Freescale Semiconductor, Inc.
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