mc68331cpv20b1 Freescale Semiconductor, Inc, mc68331cpv20b1 Datasheet - Page 105

• Manufacturer Part Number: mc68331cpv20b1
• Description: Mc68331 32 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

5.2.2 Address Registers
MC68331
USER’S MANUAL
BYTE
31
16-BIT WORD
31
LONG WORD
31
QUAD-WORD
63
31
31
Each address register and stack pointer is 32 bits wide and holds a 32-bit address. Ad-
dress registers cannot be used for byte-sized operands. Therefore, when an address
register is used as a source operand, either the low-order word or the entire long-word
operand is used, depending upon the operation size. When an address register is
used as the destination operand, the entire register is affected, regardless of the op-
eration size. If the source operand is a word size, it is sign-extended to 32 bits. Ad-
dress registers are used primarily for addresses and to support address computation.
The instruction set includes instructions that add to, subtract from, compare, and move
the contents of address registers. Figure 5-5 shows the organization of addresses in
address registers.
31
31
MSB
HIGH-ORDER BYTE
30
MSB
Figure 5-5 Address Organization in Address Registers
HIGH-ORDER WORD
SIGN EXTENDED
Figure 5-4 Data Organization in Data Registers
24 23
Freescale Semiconductor, Inc.
62
For More Information On This Product,
MIDDLE HIGH BYTE
FULL 32-BIT ADDRESS OPERAND
CENTRAL PROCESSING UNIT
ANY Dy
Go to: www.freescale.com
LONG WORD
16 15
16 15
16 15
MIDDLE LOW BYTE
ANY Dx
16-BIT ADDRESS OPERAND
LOW-ORDER WORD
8 7
1
LOW-ORDER BYTE
LSB
1
LSB
32
0
0
0
0
0
0
0
5-5
5