Central Processor Unit (CPU) Registers
Core Configuration
4
-13
11–10
S[1–0]
0
Scaling Mode
Specify the scaling to be performed in the Data ALU shifter/limiter and the
rounding position in the Data ALU MAC unit. The Shifter/limiter Scaling
mode affects data read from the A or B accumulator registers out to the
X-data bus (XDB) and Y-data bus (YDB). Different scaling modes can be
used with the same program code to allow dynamic scaling. One
application of dynamic scaling is to facilitate block floating-point arithmetic.
The scaling mode also affects the MAC rounding position to maintain
proper rounding when different portions of the accumulator registers are
read out to the XDB and YDB. Scaling mode bits are cleared at the start of
a long Interrupt Service Routine and during a hardware reset.
S1
S0
Scaling
Mode
Rounding Bit
SEquation
0
0
No scaling
23
S = (A46 XOR A45)
OR (B46 XOR B45)
OR S (previous)
0
1
Scale down
24
S = (A47 XOR A46)
OR (B47 XOR B46)
OR S (previous)
1
0
Scale up
22
S = (A45 XOR A44)
OR (B45 XOR B44)
OR S (previous)
1
1
Reserved
—
S undefined
9–8
I[1–0]
11
Interrupt Mask
Reflect the current Interrupt Priority Level (IPL) of the processor and
indicate the IPL needed for an interrupt source to interrupt the processor.
The current IPL of the processor can be changed under software control.
The interrupt mask bits are set during hardware reset, but not during
software reset.
Priority
I1
I0
Exceptions
Permitted
Exceptions Masked
Lowest
0
0
IPL 0, 1, 2, 3
None
0
1
IPL 1, 2, 3
IPL 0
1
0
IPL 2, 3
IPL 0, 1
Highest
1
1
IPL 3
IPL 0, 1, 2
7
S
0
Scaling
Set when a result moves from accumulator A or B to the XDB or YDB buses
(during an accumulator to memory or accumulator to register move) and
remains set until explicitly cleared; that is, the S bit is a
sticky bit. The
logical equations of this bit are dependent on the Scaling mode. The scaling
bit is set if the absolute value in the accumulator, before scaling, is > 0.25 or
< 0.75.
Table 4-2. Status Register Bit Definitions (Continued)
Bit Number
Bit Name
Reset Value
Description
Summary of Contents for DSP56303
Page 1: ...DSP56303 User s Manual 24 Bit Digital Signal Processor DSP56303UM AD Revision 1 January 2001 ...
Page 52: ...JTAG OnCE Interface 2 22 DSP56303 User s Manual ...
Page 114: ...General Purpose Input Output GPIO 5 10 DSP56303 User s Manual ...
Page 212: ...GPIO Signals and Registers 8 26 DSP56303 User s Manual ...
Page 268: ...Interrupt Equates A 22 DSP56303 User s Manual ...
Page 306: ...Programming Sheets B 38 DSP56303 User s Manual ...
Page 320: ...Index 14 DSP56303 User s Manual ...