ADAV400 Analog Devices, ADAV400 Datasheet - Page 21

• Manufacturer Part Number: ADAV400
• Description: Audio Codec
• Manufacturer: Analog Devices

Settings
00
01
10
11
Table 14. Target/Slew RAM Ramp Type Settings
The following sections detail how the control port writes to the
target/slew RAM to control the time constant and ramp type
parameters.
Ramp Types [1:3]—Linear, Constant dB, RC (34-Bit Write)
The target word for the first three ramp types is broken into
three parts. The 34-bit command is written with six leading 0s
to extend the data write to five bytes. The parts of the target
RAM write are
•
•
•
Ramp Type 4—Constant Time (34-Bit Write)
The target word for the constant time ramp type is written in
five parts, with the 34-bit command written with six leading 0s
to extend the data write to five bytes. The parts of the constant
time target RAM write are
•
•
•
•
•
Target/Slew RAM Initialization
On reset, the target/slew RAM initializes to preset values. The
target RAM initializes to a linear ramp type with a time constant
of 5 and the data set to 1.0. The slew RAM initializes to a value
of 1.0. These defaults result in a full-scale (1.0 to 0.0) ramp time
of 21.3 ms.
Ramp type (2 bits).
Time constant (4 bits).
Data (28 bits): 5.23 format.
Ramp type (2 bits).
Update step (1 bit). Set to 1 when a new target is loaded to
trigger a step value update. The value is automatically reset
after the step value is updated.
Number of steps (3 bits). The number of steps needed to
slew to the target value is set by these three bits, with the
number of steps equal to 2
Data (16 bits): 2.14 format.
Reserved (12 bits). When writing to the RAM, set all of
these bits to 0.
000 = 64
001 = 128
010 = 256
011 = 512
100 = 1024
101 = 2048
110 = 4096
111 = 8196
0000 = fastest
1111 = slowest
3-bit setting + 6
Ramp Type
Linear
Constant dB
RC
Constant time
.
Rev. 0 | Page 21 of 36
Linear Update
A linear update is the addition or subtraction of a constant value,
referred to as a step. The equation to describe this step size is
The result of the equation is normalized to a 5.23 data format.
This produces a time constant range from 6.75 ms to 213.4 ms.
(–60 dB relative to 0 dB full scale). An example of this kind of
update is shown in Figure 23 and Figure 24. All slew RAM figure
examples, except the half-scale constant time ramp plot (Figure
29), show an increasing or decreasing ramp between –80 dB and
0 dB (full scale). All figures except the constant time plots
(Figure 28 and Figure 29) use a time constant of 0x7 (0x0 being
the fastest and 0xF being the slowest).
Step
–0.2
–0.4
–0.6
–0.8
–1.0
–0.2
–0.4
–0.6
–0.8
–1.0
1.0
0.8
0.6
0.4
0.2
1.0
0.8
0.6
0.4
0.2
0
Figure 24. Slew RAM—Linear Update Decreasing Ramp
Figure 23. Slew RAM—Linear Update Increasing Ramp
0
=
0
0
10
2
×
(
t
2
CONST
20
5
13
5
−
5
)
10
10
15
TIME (ms)
15
TIME (ms)
20
20
25
25
ADAV400
30
30
35
35