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XC2200 Derivatives
System Units (Vol. 1 of 2)
Central Processing Unit (CPU)
User’s Manual
4-72
V2.1, 2008-08
CPUSV2_X, V2.2
MSL-Flag:
The MSL-flag is set if an automatic saturation of the accumulator has
happened. The automatic saturation is enabled if bit MS in register MCW is set. The
MSL-Flag can be also set by instructions which limit the contents of the accumulator. If
the accumulator has been limited, the MSL-Flag is set.
The MSL-Flag is a ‘Sticky Bit’. Once set, it cannot be affected by the other MAC
operations. Only a direct write operation can clear the MSL-flag.
MV-Flag:
The addition, subtraction, and accumulation operations set the MV-flag to 1 if
the result exceeds the maximum range of signed numbers (80’0000’0000
H
to
7F’FFFF’FFFF
H
); otherwise, the MV-flag is cleared. Note that if the MV-flag indicates an
arithmetic overflow, the result of the integer addition, integer subtraction, or
accumulation is not valid.
4.9.11
The Repeat Counter MRW
The Repeat Counter MRW controls the number of repetitions a loop must be executed.
The register must be pre-loaded before it can be used with -USRx CoXXX operations.
MAC operations are able to decrement this counter. When a -USRx CoXXX instruction
is executed, MRW is checked for zero
before
being decremented. If MRW equals zero,
bit USRx is set and MRW is not further decremented. Register
MRW
can be accessed
via any instruction capable of accessing a SFR.
All CoXXX instructions have a 3-bit wide repeat control field ‘rrr’ (bit positions [31:29]) in
the operand field to control the MRW repeat counter.
lists the possible
encodings.
MRW
MAC Repeat Word
SFR (FFDA
H
/ED
H
)
Reset Value: 0000
H
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
REPEAT_COUNT
rwh
Field
Bits
Type
Description
REPEAT_
COUNT
[15:0]
rwh
16-bit loop counter