MPC555
/
MPC556
EXTERNAL BUS INTERFACE
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
9-37
9.5.7.5 Transfer Size
The transfer size signals (TSIZ[0:1]) indicate the size of the requested data transfer.
During each transfer, the TSIZ signals indicate how many bytes are remaining to be
transferred by the transaction. The TSIZ signals can be used with BURST and AD-
DR[30:31] to determine which byte lanes of the data bus are involved in the transfer.
For nonburst transfers, the TSIZ signals specify the number of bytes starting from the
byte location addressed by ADDR[30:31]. In burst transfers, the value of TSIZ is al-
ways 00.
9.5.7.6 Address Types
The address type (AT[0:3]), program trace (PTR), and reservation transfer (RSV) sig-
nals are outputs that indicate one of 16 address types. These types are designated as
either a normal or alternate master cycle, user or supervisor, and instruction or data
type. The address type signals are valid at the rising edge of the clock in which the
special transfer start (STS) signal is asserted.
A special use of the PTR and RSV signals is for the reservation protocol described in
.
Refer to
9.5.13 Show Cycle Transactions
for informa-
tion on show cycles.
summarizes the pins used to define the address type.
lists all the
definitions achieved by combining these pins.
Table 9-6 BURST/TSIZE Encoding
BURST
TSIZ(0:1)
Transfer Size
Negated
01
Byte
Negated
10
Half-word
Negated
11
x
Negated
00
Word
Asserted
00
Burst (16 bytes)
Table 9-7 Address Type Pins
Pin
Function
STS
0 = Special transfer
1 = Normal transfer
TS
0 = Start of transfer
1 = No transfer
AT0
Must equal zero on MPC555 /
MPC556
AT1
0 = Supervisor mode
1 = User mode
AT2
0 = Instruction
1 = Data
AT3
Reservation/Program Trace
PTR
0 = Program trace
1 = No program trace
RSV
0 = Reservation data
1 = No reservation
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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