Renesas M65881AFP manual Mantissa Data decimal value 128

M65881AFP

The index and Mantissa part of Gain Data (bit12-bit24 :GAIN0-GAIN12)

The gain value is set from bit12-bit24. Index part: bit12(MSB) to bit16(LSB)

Mantissa part: bit17(MSB) to bit24(LSB)

The gain data is assigned 13bits, composed of Index part 5bits and of Mantissa part 8bits.

The range of Index parts is following statements.

Index part: 10100b(16.0) to 10000b(1.0) to 00000b(2-16)

The range of Mantissa parts is following statements.

Mantissa part:Index part; 10100b to 00001b: Mantissa part; 11111111b to 10000000b (128 step/ Index).

Index part; 00000b:Mantissa part; 11111111b to 00000000b (256 step).

Initial value: Index part: 10000b	Mantissa part: 10000000b
Infinity zero: Index part: 00000b	Mantissa part: 00000000b

# Notice of GAIN value setting continuously

In case of Gain value setting continuously, for example of setting L/Rch independently, please take the interval time (pulse interval time of SCLATCH signal) more than 1/fso. For example, in the case of fso=48kHz, please take the interval time more than 21µsec.

• The Gain Data and Audio Output Level.

Gain data consists of 13bits (Index part: 5bit, Mantissa part: 8bit ). e.g. 10000b(1.0)/10000000b(0.5) means 0.5(0dB).

Table 1-2 Gain data and output level

Gain Data		Polarity
10100/11111111	(b)
~
10001/10000000	(b)
~
10000/10000000	(b)
01111/11111111	(b)	+
~
00000/10000000	(b)
~
00000/00000001	(b)
00000/00000000	(b)

Output absolute	Output Level
maximum value
15.9375	+30.069dB
~	~
1.0	+6.021dB
~	~
0.5	0dB
0.498046875	-0.0340dB
~	~
0.5 ∗ 2-16	-96.330dB
~	~
0.00390625 ∗ 2-16	-138.474dB
infinity zero

• Calculation method of Gain Value

The way to calculation of Gain value from Gain Data is following equation.

Gain value = 20log [ 2	<Index data (decimal value)-16>	×	Mantissa Data (decimal value)	] dB
			128

Rev.1.00 2003.05.08 page 14 of 23