Analog Devices ADAV4601, Документ по проектированию системы

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ADAV4601 System Design Document Confidential Information
Rev.1 August 2009 Analog Devices Page 43
CHANGING THE VOLUME
The volume works by multiplying the decimal contents of the volume control register by the signal. The volume
control is a 28-bit word in 5.23 two’s complement format. The ADAV4601 uses 16-bit registers therefore the volume
control must be spread over two registers. The figure below graphically illustrates how this is arranged.
Figure 35. 28-Bit word across two 16-bit registers
To simplify updating the volume control, the I
2
C address pointer auto-increments when writing and reading. This
means that the volume control register can be updated in a single I 2 C block write. Therefore, it is recommended that
the volume control is updated using the following I
2
C write format:
<device address> <0114> <32-bit data transfer>
Note that the volume control is a 32-bit parameter; therefore, both Register 0x0114 and Register 0x0115 must be
written to. Writing anything less than the 32 bits to these registers will not update the parameter.
The default volume is 1 or 0dB which cause no change to the signal. The I
2
C write for this is:
34 0114 00800000
EXAMPLE: INCREASE THE MAIN VOLUME TO +6DB OVER DEFAULT
1. The volume works by multiplying the decimal contents of the register by the signal. Therefore in order to
increase by 6dB, the multiplication factor equivalent to 6dB must be found. Using some algebra this can
be easily found.
dB x Log 6 20
10
=
20
6
10
=
x Log
20
6
10
=
x
995262315 . 1
=
x