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MOTOROLA
MC68349 USER’S MANUAL
5- 15
5.3.2 Registers
Registers D7–D0 are used as data registers for bit, byte (8-bit), word (16-bit), long-word
(32-bit), and quad-word (64-bit) operations. Registers A6 to A0 and the USP and SSP are
address registers that may be used as software SPs or base address registers. Register
A7 (shown as A7 and A7' in Figures 5-8 and 5-9) is a register designation that applies to
the USP in the user privilege level and to the SSP in the supervisor privilege level. In
addition, address registers may be used for word and long-word operations. All 16
general-purpose registers (D7–D0, A7–A0) may be used as index registers.
The PC contains the address of the next instruction to be executed by the CPU32+.
During instruction execution and exception processing, the processor automatically
increments the contents of the PC or places a new value in the PC, as appropriate.
The SR (see Figure 5-10) contains condition codes, an interrupt priority mask (three bits),
and three control bits. Condition codes reflect the results of a previous operation. The
codes are contained in the low byte (condition code register (CCR)) of the SR. The
interrupt priority mask determines the level of priority an interrupt must have to be
acknowledged. The control bits determine trace mode and privilege level. At user privilege
level, only the CCR is available. At supervisor privilege level, software can access the full
SR.
The VBR contains the base address of the exception vector table in memory. The
displacement of an exception vector is added to the value in this register to access the
vector table.
Alternate source and destination function code registers (SFC and DFC) contain 3-bit
function codes. The CPU32+ generates a function code each time it accesses an address.
Specific codes are assigned to each type of access. The codes can be used to select
eight dedicated 4-Gbyte address spaces. The MOVEC instruction can use registers SFC
and DFC to specify the function code of a memory address.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
T1
T0
S
0
I2
I1
I0
0
X
N
Z
V
C
EXTEND
NEGATIVE
ZERO
OVERFLOW
CARRY
INTERRUPT
PRIORITY MASK
SUPERVISOR/USER
STATE
TRACE
ENABLE
SYSTEM BYTE
USER BYTE
(CONDITION CODE REGISTER)
Figure 5-10. Status Register