Memory Map/Register Set

The additional MAC status register (MACSR) contains a 4-bit operational mode field and condition flags. Operational mode bits control whether operands are signed or unsigned and whether they are treated as integers or fractions. These bits also control the overflow/saturation mode and the way in which rounding is performed. Negative, zero, and multiple overflow condition flags are also provided.

3.4Memory Map/Register Set

The EMAC provides the following program-visible registers:

Four 32-bit accumulators (ACCn = ACC0, ACC1, ACC2, and ACC3)

Eight 8-bit accumulator extensions (two per accumulator), packaged as two 32-bit values for load and store operations (ACCext01 and ACCext23)

One 16-bit mask register (MASK)

One 32-bit MAC status register (MACSR) including four indicator bits signaling product or accumulation overflow (one for each accumulator: PAV0–PAV3)

These registers are shown in Figure 3-6.

31

0

MACSR

MAC status register

 

 

 

 

 

 

ACC0

MAC accumulator 0

 

 

 

 

 

 

ACC1

MAC accumulator 1

 

 

 

 

 

 

ACC2

MAC accumulator 2

 

 

 

 

 

 

ACC3

MAC accumulator 3

 

 

 

 

 

 

ACCext01

Extensions for ACC0 and ACC1

 

 

 

 

 

 

ACCext23

Extensions for ACC2 and ACC3

 

 

 

 

 

 

MASK

MAC mask register

 

 

 

 

 

 

 

 

Figure 3-6. EMAC Register Set

3.4.1MAC Status Register (MACSR)

MACSR functionality is organized as follows:

MACSR[11–8] contains one product/accumulation overflow flag per accumulator.

MACSR[7–4] defines the operating configuration of the MAC unit.

MACSR[3–0] contains indicator flags from the last MAC instruction execution.

Bit

31

12

11–8

7

6

5

4

3

2

1

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Prod/acc overflow flags

Operational Mode

 

Flags

 

 

 

 

 

 

 

 

 

 

 

 

 

Field

 

PAVx

OMC

S/U

F/I

R/T

N

Z

V

EV

 

 

 

 

 

 

 

 

 

 

 

 

Reset

 

0000_0000_0000_0000_0000_0000_0000_0000

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R/W

 

 

R/W

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3-7. MAC Status Register (MACSR)

Table 3-1describes MACSR fields.

3-6

MCF5282 User’s Manual

MOTOROLA

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Motorola MCF5282, MCF5281 user manual Memory Map/Register Set, MAC Status Register Macsr, 1describes Macsr fields