ColdFire Core
7-8
Freescale Semiconductor
MCF51CN128 Reference Manual, Rev. 6
7.2.8
Status Register (SR)
The SR stores the processor status and includes the CCR, the interrupt priority mask, and other control
bits. In supervisor mode, software can access the entire SR. In user mode, only the lower 8 bits (CCR) are
accessible. The control bits indicate the following states for the processor: trace mode (T bit), supervisor
or user mode (S bit), and master or interrupt state (M bit). All defined bits in the SR have read/write access
when in supervisor mode. The lower byte of the SR (the CCR) must be loaded explicitly after reset and
before any compare (CMP), Bcc, or Scc instructions execute.
27
BWD
Buffered write disable. The ColdFire core is capable of marking processor memory writes as bufferable or
non-bufferable.
0 Writes are buffered and the bus cycle is terminated immediately with zero wait states.
1 Disable the buffering of writes. In this configuration, the write transfer is terminated based on the response time
of the addressed destination memory device.
Note:
If buffered writes are enabled (BWD = 0), any error status is lost as the immediate termination of the data
transfer assumes an error-free completion.
26
Reserved, must be cleared.
25
FSD
Flash speculation disabled. Disables certain performance-enhancing features related to address speculation in the
flash memory controller.
0 The flash controller tries to speculate on read accesses to improve processor performance by minimizing the
exposed flash memory access time. Recall the basic flash access time is two processor cycles.
1 Certain flash address speculation is disabled.
24
CBRR
Crossbar round-robin arbitration enable. Configures the crossbar slave ports to fixed-priority or round-robin
arbitration.
0 Fixed-priority arbitration
1 Round robin arbitration
23–0
Reserved, must be cleared.
BDM: Load: 0xEE (SR)
Store: 0xCE (SR)
Access: Supervisor read/write
BDM read/write
System Byte
Condition Code Register (CCR)
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
R
T
0
S
M
0
I
0
0
0
X
N
Z
V
C
W
Reset
0
0
1
0
0
1
1
1
0
0
0
—
—
—
—
—
Figure 7-9. Status Register (SR)
Table 7-4. SR Field Descriptions
Field
Description
15
T
Trace enable. When set, the processor performs a trace exception after every instruction.
14
Reserved, must be cleared.
Table 7-3. CPUCR Field Descriptions (continued)
Field
Description