ST20-C1 datasheet(66/205 Pages) STMICROELECTRONICS

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5.7 Data formats

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A Q15 value in a 16-bit field is organiz ed as shown in Figure 5.7.

Figure 5.7 Q15 data format (16-bits)

The minimum and maximum representable values are as shown in Table 5.9.

5.7.5

Q15 in an oversized field

When a Q15 value is stored in an oversized field, e .g.a 32-bit register, the significant

bits are placed at the least significant end of the field, and the v alue is sign-extended

to the width of the whole field.

The value still has the same range (-1

≤ n < 1) and the same number of significant

bits.

A Q15 value in a 32-bit field is organiz ed as shown in Figure 5.8.

Figure 5.8 Q15 data format (32-bits)

The minimum and maximum representable values are as shown in Table 5.10.

Hex Value

Decimal Value

Minimum

8000

-1

Maximum

7FFF

+0.9999

Table 5.9 Q15 limiting values

2-1

-(20)2-2

2-3

2-14

2-15

binary point

sign bit

Bit position

Most significant

Least significant

-(20)

-(20)2-1

2-14

2-13

2-15

binary point

sign bit

Bit position

Most significant

Least significant

Basic Q15 value

sign extended

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