Motorola DSP96002 User Manual

Page 763

MOTOROLA

DSP96002 USER’S MANUAL

D-11

formats to/from the DP storage format in the data ALUs register file. The conversion is depicted in Figure

D-10 and is done in a transparent fashion.

When moving SP numbers into the data ALU, the 52-bit fraction of the DP internal format is written with the

23-bit fraction of the source in its most significant bits, and the implicit integer bit is made explicit. The re-

maining bits of the fraction are set equal to zero. If the number in question is denormalized (exponent = e

min

and the first bit of the mantissa = 0), the U tag is set. In the non-IEEE "flush to zero" mode (indicated by the

FZ bit in the Status Register), the number is considered zero when used as an operand for floating-point

operations, although the contents of the register are not changed. In the IEEE mode, the number is "cor-

rected" when used as an operand for floating point calculations, at the expense of extra cycles introduced

for normalization.

The 8-bit exponent of the SP source is translated into an 11-bit exponent by copying the 7 least significant

bits of the source exponent into the seven least significant bits of the destination. The most significant bit of

the 8-bit exponent of the source is copied to the most significant bit of the exponent of the destination. The

31 30 29

Fraction

23 22

95 94 74 73 72 71

63 62

32 31

11 10

(3)

Fraction

X or Y Data Memory

i = 1 when normalized
i = 0 when unnormalized

(2)

Figure D-10a. Automatic Format Conversion – Single Precision

40 39

31 30 29

Fraction

23 22

X or Y Data Memory

† †

†

(1)

Notes: * –

† – When NaN bits 71, 72, 73 = 1
When not NaN Bit 74

↔

Bit 30

Bits 73, 72, 71 are complement

of Bit 74.

(1) – Bits 32-39 are nonzero when the register
contains a SEP floating point result or a
DP floating point number.
Bits 32-39 are zero when the register
contains a SP floating point number.

(2) – Bits 11-31 are only nonzero when the

(3) – Bits 0-10 are always zero when
representing a floating point number.