CM-42 Technical Description
PAGE 17 OF 38
SEM/CX-02:0076/DES A
ATMS
:
An application using the analog audio interface must re-reference the signal from its own internal BIAS to
AGND. The figure below shows an example of a microphone implementation.
The microphone should preferably be connected to its pre-amplifier differentially, which will minimize noise pickup
from possible ground current.
AFMS
:
An application using the
analog audio interface must re-
reference the AFMS-signal from
AGND to its own internal BIAS.
The figure shows a differential
implementation. C1 is chosen to
create the correct HP frequency
response. R1 and R2 determine
the gain, and C2 and R2
determine the LP frequency
response.
2.3.4.2 Digital Audio
The CM-42 provides digital audio capability over the system connector. The digital audio signals enable the
connection of a digital audio source. The receiver is bypassing the analog audio processing functions performed
within the module. The digital audio interface includes the following PCM signals:
Pin
CM-42
Description
17
PCMCLK
PCM Clock Output from module.
18
PCMSYNC
PCM Frame Sync from module
19
PCMDLD
PCM Voice Output from module.
20
PCMULD
PCM Voice Input to module.
Table 11: CM-42 Digital Audio Signals
Already defined CMOS output/input electrical characteristics apply (see Section 2.3.2 above).
The PCM format (for
PCMULD and PCMDLD
) follows a linear PCM data format with 13-bit data embedded in a 16-
bit word. The data bits in
PCMULD
(input) and
PCMDLD
(output) are aligned so that the MSB in each word occurs
on the same clock edge. See timing diagram in Figure 6.
0
-
+
0
VCC
0
-
+
0
<=1k
BIAS
>=2.2uF
ATMS
AGND
>=2.2uF
+
+
0
-
+
0
R1
>=10k
R1
>=10k
R2
R2
C1
C1
C2
C2
BIAS
AFMS
AGND
Internal App +
Internal App -
