adav400kstz-reel Analog Devices, Inc., adav400kstz-reel Datasheet - Page 21

• Manufacturer Part Number: adav400kstz-reel
• Description: Audio Codec With Embedded Sigmadsp Processor
• Manufacturer: Analog Devices, Inc.

Table 14. Target/Slew RAM Ramp Type Settings
Settings
00
01
10
11
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 (two bits).
Time constant (four bits).
0000 = fastest
Data (28 bits): 5.23 format.
Ramp type (two bits).
Update step (one 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 (three 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.
1111 = slowest
000 = 64
001 = 128
010 = 256
011 = 512
100 = 1024
101 = 2048
110 = 4096
111 = 8196
3-bit setting + 6
Ramp Type
Linear
Constant dB
RC
Constant time
.
Rev. A | 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
examples, except the half-scale constant time ramp plot (Figure
29
0 dB (full scale). All figures except the constant time plots
(
the fastest, and 0xF being the slowest).
Figure 28 and Figure 29) use a time constant of 0x7 (0x0 being
), show an increasing or decreasing ramp between –80 dB and
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
Figure 23 and Figure 24. All slew RAM figure
−
5
)
10
10
15
TIME (ms)
15
TIME (ms)
20
20
25
25
ADAV400
3
0
3
0
35
35