mpc823rg Freescale Semiconductor, Inc, mpc823rg Datasheet - Page 331

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mpc823rg

Manufacturer Part Number
mpc823rg
Description
Mpc823 Powerquicc Integrated Communications Processor For Portable Systems
Manufacturer
Freescale Semiconductor, Inc
Datasheet
13.4.5 Transfer Alignment and Packaging
The MPC823 external bus only supports natural address alignment that forces the following
restrictions:
The MPC823 can perform operand transfers through its 32-bit data port. If the transfer is
controlled by the internal memory controller, the MPC823 can support 8- and 16-bit data port
sizes. The bus requires that the portion of the data bus used for a transfer to or from a
particular port size to be fixed. A 32-bit port must reside on data bus bits 0-31, a 16-bit port
must reside on bits 0-15, and an 8-bit port must reside on bits 0-7. The MPC823 always tries
to transfer the maximum amount of data on all bus cycles and for a word operation it always
assumes that the port is 32 bits wide at the beginning of the bus cycle. In Figure 13-18 and
Figure 13-19 and Table 13-2 and Table 13-3, the following operand conventions have been
adopted:
• Byte access can have any address alignment
• Half-word access must have address bit 31 equal to 0
• Word access must have address bits 30-31 equal to 0
• For burst access must have address bits 30-31 equal to 0
• OP0 is the most-significant byte of a word operand and OP3 is the least-significant byte.
• The two bytes of a half-word operand are OP0 (most-significant) and OP1 or OP2
• The single byte of a byte-length operand is OP0, OP1, OP2, or OP3, depending on the
(least-significant) and OP3, depending on the address of the access.
address of the access.
0
Note: Although this is a 32-bit machine, only 26 of the bits are visible outside the chip.
OP0
OP0
OP0
Figure 13-18. Internal Operand Representation
Freescale Semiconductor, Inc.
For More Information On This Product,
OP1
OP1
OP1
MPC823 REFERENCE MANUAL
Go to: www.freescale.com
OP2
OP2
OP2
OP3
OP3
31
WORD
HALF-WORD
BYTE
External Bus Interface
13-25

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