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ColdFire Core
MCF5272 ColdFire
®
Integrated Microprocessor User’s Manual, Rev. 3
2-10
Freescale Semiconductor
2.4
Organization of Data in Registers
The following sections describe data organization within the data, address, and control registers.
2.4.1
Organization of Integer Data Formats in Registers
shows the integer format for data registers. Each integer data register is 32 bits wide. Byte and
word operands occupy the lower 8- and 16-bit portions of integer data registers, respectively. Longword
operands occupy the entire 32 bits of integer data registers. A data register that is either a source or
destination operand only uses or changes the appropriate lower 8 or 16 bits in byte or word operations,
respectively. The remaining high-order portion does not change. The least significant bit (lsb) of all integer
sizes is zero, the most-significant bit (msb) of a longword integer is 31, the msb of a word integer is 15,
and the msb of a byte integer is 7.
The instruction set encodings do not allow the use of address registers for byte-sized operands. When an
address register is a source operand, either the low-order word or the entire longword operand is used,
depending on the operation size. Word-length source operands are sign-extended to 32 bits and then used
in the operation with an address register destination. When an address register is a destination, the entire
register is affected, regardless of the operation size.
shows integer formats for address registers.
The size of control registers varies according to function. Some have undefined bits reserved for future
definition by Freescale. Those particular bits read as zeros and must be written as zeros for future
compatibility.
All operations to the SR and CCR are word-size operations. For all CCR operations, the upper byte is read
as all zeros and is ignored when written, regardless of privilege mode.
31
30
1
0
msb
lsb
Bit (0 ð bit number ð 31)
31
8
7
6
1
0
Not used
msb
Low order byte
lsb
Byte (8 bits)
31
16
15
14
1
0
Not used
msb
Lower order word
lsb
Word (16 bits)
31
30
1
0
msb
Longword
lsb
Longword (32 bits)
Figure 2-7. Organization of Integer Data Formats in Data Registers
31
16
15
0
Sign-Extended
16-Bit Address Operand
31
0
Full 32-Bit Address Operand
Figure 2-8. Organization of Integer Data Formats in Address Registers
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