MC68332
CENTRAL PROCESSING UNIT
USER’S MANUAL
5-5
5.2.2 Address Registers
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.
shows the organization of addresses in
address registers.
Figure 5-5 Address Organization in Address Registers
5.2.3 Program Counter
The PC contains the address of the next instruction to be executed by the CPU32. Dur-
ing instruction execution and exception processing, the processor automatically incre-
ments the contents of the PC or places a new value in the PC as appropriate.
5.2.4 Control Registers
The control registers described in this section contain control information for supervi-
sor functions and vary in size. With the exception of the condition code register (the
user portion of the status register), they are accessed only by instructions at the su-
pervisor privilege level.
5.2.4.1 Status Register
The status register (SR) stores the processor status. It contains the condition codes
that reflect the results of a previous operation and can be used for conditional instruc-
tion execution in a program. The condition codes are extend (X), negative (N), zero
(Z), overflow (V), and carry (C). The user (low-order) byte containing the condition
codes is the only portion of the SR information available at the user privilege level; it
is referenced as the condition code register (CCR) in user programs.
At the supervisor privilege level, software can access the full status register. The upper
byte of this register includes the interrupt priority (IP) mask (three bits), two bits for
placing the processor in one of two tracing modes or disabling tracing, and the super-
visor/user bit for placing the processor at the desired privilege level.
Undefined bits in the status register are reserved by Freescale for future definition. The
undefined bits are read as zeros and should be written as zeros for future compatibility.
31
16 150
SIGN EXTENDED
16-BIT ADDRESS OPERAND
31
0
FULL 32-BIT ADDRESS OPERAND
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Freescale Semiconductor, Inc.
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