Datasheet

Chapter 2. ColdFire Core 2-13
Integer Data Formats
2.3 Integer Data Formats
Table 2-4 lists the integer operand data formats. Integer operands can reside in registers,
memory, or instructions. The operand size for each instruction is either explicitly encoded
in the instruction or implicitly defined by the instruction operation.
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
Figure 2-7 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
Table 2-4. Integer Data Formats
Operand Data Format Size
Bit 1 bit
Byte integer 8 bits
Word integer 16 bits
Longword integer 32 bits
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