MOTOROLA
Chapter 13. External Interface Module (EIM)
13-15
Misaligned Operands
misaligned at an odd address, and a longword is misaligned at an address not a multiple of
four. Although the MCF5282 enforces no alignment restrictions for data operands
(including program counter (PC) relative data addressing), additional bus cycles are
required for misaligned operands.
Instruction words and extension words (opcodes) must reside on word boundaries.
Attempting to prefetch a misaligned instruction word causes an address error exception.
The MCF5282 converts misaligned, cache-inhibited operand accesses to multiple aligned
accesses. Figure 13-19 shows the transfer of a longword operand from a byte address to a
32-bit port. In this example, SIZ[1:0] specify a byte transfer and a byte offset of 0x1. The
slave device supplies the byte and acknowledges the data transfer. When the MCF5282
starts the second cycle, SIZ[1:0] specify a word transfer with a byte offset of 0x2. The next
two bytes are transferred in this cycle. In the third cycle, byte 3 is transferred. The byte
offset is now 0x0, the port supplies the final byte, and the operation is complete.
Figure 13-19. Example of a Misaligned Longword Transfer (32-Bit Port)
If an operand is cacheable and is misaligned across a cache-line boundary, both lines are
loaded into the cache. The example in Figure 13-20 differs from that in Figure 13-19 in that
the operand is word-sized and the transfer takes only two bus cycles.
Figure 13-20. Example of a Misaligned Word Transfer (32-Bit Port)
Transfer 1
Transfer 2
Transfer 3
—
—
Byte 3
Byte 0
—
—
—
Byte 1
—
—
Byte 2
—
31
24 23
16 15
8 7
0
001
010
100
A[2:0]
Transfer 1
Transfer 2
—
Byte 1
—
—
—
—
Byte 0
—
31
24 23
16 15
8 7
0
001
100
A[2:0]
Summary of Contents for ColdFire MCF5281
Page 124: ...3 20 MCF5282 User s Manual MOTOROLA EMAC Instruction Set Summary ...
Page 141: ...MOTOROLA Chapter 5 Static RAM SRAM 5 5 SRAM Programming Model ...
Page 142: ...5 6 MCF5282 User s Manual MOTOROLA SRAM Programming Model ...
Page 168: ...6 26 MCF5282 User s Manual MOTOROLA Interrupts ...
Page 186: ...7 18 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 228: ...9 22 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 246: ...10 18 MCF5282 User s Manual MOTOROLA Low Power Wakeup Operation ...
Page 254: ...11 8 MCF5282 User s Manual MOTOROLA Memory Map and Registers ...
Page 264: ...12 10 MCF5282 User s Manual MOTOROLA Chip Select Registers ...
Page 280: ...13 16 MCF5282 User s Manual MOTOROLA Misaligned Operands ...
Page 314: ...14 34 MCF5282 User s Manual MOTOROLA MCF5282 External Signals ...
Page 339: ...MOTOROLA Chapter 15 Synchronous DRAM Controller Module 15 25 SDRAM Example ...
Page 340: ...15 26 MCF5282 User s Manual MOTOROLA SDRAM Example ...
Page 356: ...16 16 MCF5282 User s Manual MOTOROLA DMA Controller Module Functional Description ...
Page 408: ...17 52 MCF5282 User s Manual MOTOROLA Buffer Descriptors ...
Page 446: ...20 24 MCF5282 User s Manual MOTOROLA Interrupts ...
Page 474: ...22 18 MCF5282 User s Manual MOTOROLA Programming Model ...
Page 510: ...23 36 MCF5282 User s Manual MOTOROLA Operation ...
Page 526: ...24 16 MCF5282 User s Manual MOTOROLA I2C Programming Examples ...
Page 672: ...28 12 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 718: ...29 46 MCF5282 User s Manual MOTOROLA Motorola Recommended BDM Pinout ...
Page 750: ...32 8 MCF5282 User s Manual MOTOROLA Ordering Information ...