SM5844 NPC [Nippon Precision Circuits Inc], SM5844 Datasheet - Page 15

• Manufacturer Part Number: SM5844
• Description: Asynchronous Sample Rate Converter
• Manufacturer: NPC [Nippon Precision Circuits Inc]

Attenuation (MDT, MCK, MLEN)
The digital attenuator coefficients are read in as
serial data on the microcontroller interface. Data on
MDT is read into the internal shift register on the
rising edge of MCK, and then 12 bits are latched
internally on the rising edge of MLEN.
Although the attenuation data comprises 11 bits,
only 1025 levels are valid as given by the following.
The gain of the attenuator for values of DATT from
001H to 400H are given by the following equations.
Note that when the F12DB flag is HIGH, the gain is
shifted by +12.0412 dB.
Table 5. Attenuator settings
DATT
Attenuation data DAT T
400H (to 7FFH)
MLEN
MCK
MDT
=
0 0 0 H
0 0 1 H
1 0 0 H
3 F F H
i
10
=
0
a
i
2
10 i –
Figure 3. Attenuation data format (microcontroller interface)
LOW
Gain (dB)
B1
60.206
12.041
0.0085
0
F 1 2 D B = L OW (default)
MSB
B2
a0
B3
a1
Linear expression
SM5844AF
B4
1023/1024
a2
256/1024
1/1024
0.0
1.0
When the leading bit is 0 (B1 = LOW), the following
11 bits are read into the attenuation register and used
as an unsigned integer in MSB first format. See
figure 3.
After a system reset initialization, DATT is set to
400H and the F12DB flag is LOW, corresponding to
0 dB gain. (The F12DB flag is described in table 2.)
Gain
when F12DB = LOW
=
=
when F12DB = HIGH
B8
a6
20
20
log
log
B9
a7
Gain (dB)
12.032
12.041
48.165
0.0
DATT
--------------- -
NIPPON PRECISION CIRCUITS—15
DATT
--------------- -
MCK and MLEN can also follow the dotted lines.
1024
256
B10
a8
F 1 2 D B = H I G H
[dB]
[dB]
B11
a9
Linear expression
B12
LSB
a10
1023/256
256/256
1/256
0.0
4.0