Datasheet

2-32 MCF5307 User’s Manual
Organization of Data in Registers
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 anaddress register
destination. When an address register is a destination, the entire register is affected,
regardless of the operation size. Figure 2-8 shows integer formats for address registers.
The size of control registers varies according to function. Some have undefined bits
reserved for future definition by Motorola. 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.
2.4.2 Organization of Integer Data Formats in Memory
All ColdFire processors use a big-endian addressing scheme. The byte-addressable
organization of memory allows lower addresses to correspond to higher order bytes. The
address N of a longword data item corresponds to the address of the high-order word. The
lower order word is located at address N + 2. The address N of a word data item corresponds
to the address of the high-order byte. The lower order byte is located at address N + 1. This
31 30 1 0
msb lsb Bit (0 ≤ bit number ≤ 31)
31 7 0
Not used msb Low order byte lsb Byte (8 bits)
31 15 0
Not used msb Lower order word lsb Word (16 bits)
31 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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