XC2200 Derivatives
System Units (Vol. 1 of 2)
Central Processing Unit (CPU)
User’s Manual
4-70
V2.1, 2008-08
CPUSV2_X, V2.2
4.9.10
The MAC Unit Status Word MSW
The upper byte of register MSW (bit-addressable) shows the current status of the MAC
Unit. The lower byte of register MSW represents the 8-bit MAC accumulator extension,
building the 40-bit accumulator together with registers MAH and MAL.
MSW
MAC Status Word
SFR (FFDE
H
/EF
H
)
Reset Value: 0000
H
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
-
MV MSL ME MSV MC
MZ
MN
MAE
-
rwh rwh rwh rwh rwh rwh rwh
rwh
Field
Bits
Type
Description
MV
14
rwh
Overflow Flag
0
No Overflow produced
1
Overflow produced
MSL
13
rwh
Sticky Limit Flag
0
Result was not saturated
1
Result was saturated
ME
12
rwh
MAC Extension Flag
0
MAE does not contain significant bits
1
MAE contains significant bits
MSV
11
rwh
Sticky Overflow Flag
0
No Overflow occurred
1
Overflow occurred
MC
10
rwh
Carry Flag
0
No carry/borrow produced
1
Carry/borrow produced
MZ
9
rwh
Zero Flag
0
MAC result is not zero
1
MAC result is zero
MN
8
rwh
Negative Result
0
MAC result is positive
1
MAC result is negative
MAE
[7:0]
rwh
MAC Accumulator Extension
The most significant bits of the 40-bit accumulator,
completing registers MAH and MAL