APA3175 datasheet(21/46 Pages) ANPEC

21 / 46 page

Rev. A.3 - Aug., 2016

www.anpec.com.tw

APA3175

Function Description (Cont.)

26Bit 3.23 Number Format

All mixer gain coefficients are 26 bit coefficients and use a 3.23 number format. Numbers formatted as 3.23 numbers

means that there are 3 bits to the left of the decimal point and 23 bits to the right of the decimal point. This is shown

in Figure 18.

Figure 18. 3.23 Format

The decimal value of a 3.23 format number can be found by following the weighting and is shown in Figure 18. If the

MSB is logic 0, the number is a positive number, and the weighting shown yields the correct number. If the MSB is a

logic 1, and then the number is a negative number. In this case, every bit must be inverted, a 1 added to the result, and

then the weighting shown in Figure 19 applied to obtain the magnitude of the negative number.

Figure 19. Conversion Weighting Facroes 3.23 Format to Floating Point

Gain coefficients, entered via the I2C bus, must be entered as 32 bit binary numbers. The format of the 32 bit number

(4 byte or 8 digit hexadecimal number) is shown in Figure 20.

Figure 20. Alignment of 3.23 Coefficient in 32Bit I2C Word

2-23 Bit

20 Bit

21 Bit

2-1 Bit

2-4 Bit

(1 or 0) x21+

(1 or 0) x20+

(1 or 0) x2-1+

(1 or 0) x2-4+

(1 or 0) x2-23

S_xx.xxxx_xxxx_xxxx_xxxx_xxxx_xxx

2-23 Bit

2-5 Bit

2-1 Bit

20 Bit

21 Bit

Sign Bit

u S

Fraction

Digit 6

Fraction

Digit 5

Fraction

Digit 4

Fraction

Digit 2

Fraction

Digit 3

Fraction

Digit 1

Integer

Digit 1

Sign Bit

Coefficient

digit 8

Coefficient

digit 7

Coefficient

digit 6

Coefficient

digit 5

Coefficient

digit 4

Coefficient

digit 3

Coefficient

digit 2

Coefficient

digit 1

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