Infineon Technologies C166S V2 User Manual page 83

number (MAH has 1 in the most significant bit), the MAE will be loaded with ones,
representing the extended 40-bit negative number in 2s compliment notation. One may
see that the extended 40-bit value is equal to 32-bit value without extension. In other
words, after this extension, MAE does not contain significant bits. Generally, this
condition is present when the highest 9 bits of the 40-bit signed result are the same.
During the accumulator operations, an overflow may happen and the result may not fit
into 32-bits and the MAE will change. The extension flag "E", which is the part of the most
significant byte of MSW, is set when the signed result in the accumulator has overflowed
the 32-bit boundary. This condition is present when the highest 9 bits of the 40-bit signed
result are not the same, i.e. MAE contains significant bits.
Most CoXXX operations specify the 40-bit accumulator register as a source and/or a
destination operand.
The MAC Unit Accumulator Extension Byte MAE
The MAE register is a part of the 40-bit MAC unit accumulator register. MAE is accessed
as the Least Significant Byte of MSW. It is implicitly used by the MAC unit for MAC
operation. In case a word operand is written into MAH, the MAE register becomes sign-
extended. It can be accessed via any instruction capable of accessing an SFR.
MSW
MAC Status Word
15 14 13 12
0 MV MSL ME MSV MC
rwh rwh rwh
r
Field
MAE
The MAC Unit Accumulator High Word MAH
The MAH register is a part of the 40-bit MAC unit accumulator register. It is implicitly used
by the MAC unit for MAC operation. In case the word operand is written into MAH, MAL
acquires the zero value and the MAE register becomes sign-extended. It can be
accessed via any instruction capable of accessing an SFR.
User Manual
SFRb
11 10 9 8
MZ MN
rwh rwh rwh rwh
Bits Type Description
[7:0] rwh The most significant bits of the 40-bit Accumulator
7 6 5
2-83
User Manual
C166S V2
Central Processing Unit
Reset Value: 0000
4 3 2 1
MAE
rwh
V 1.7, 2001-01
H
0