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MC55/56 Hardware Interface Description
Confidential / Released
When shipped from factory, all audio parameters of MC55/56 are set to interface 1 and
audio mode 1. This is the default configuration optimised for the Votronic HH-SI-30.3/V1.1/0
handset and used for type approving the Siemens reference configuration. Audio mode 1
has fix parameters which cannot be modified. To adjust the settings of the Votronic handset
simply change to another audio mode.
In transmit direction, all audio modes contain internal scaling factors (digital amplification)
that are not accessible by the user. To avoid saturation with a full scale digital input signal on
the DAI, and to obtain a one-to-one digital access to the speech coder in audio mode 5
and 6, it is recommended to set the parameter <inCalibrate> of the selected audio mode as
follows:
Audio mode 1 and 4:
23196
Audio mode 2:
17396
Audio mode 3:
21901
Audio mode 5 and 6:
21402
3.10.1
Microphone circuit
Interface 1
This interface has no microphone supply circuit and therefore, has an impedance of 50kΩ.
When connecting a microphone or another signal source to interface 1 you are required to
add two 100 nF capacitors, one to each line.
Interface 2
This interface comes with a microphone supply circuit and can be used to feed an active
microphone. It has an impedance of 2kΩ. If you do not use it or if you want to connect
another type of signal source, for example, an op amp or a dynamic microphone, it needs to
be decoupled with capacitors. The power supply can be switched off and on by using the
command AT^SNFM. For details see [1].
Figure 17 shows the microphone inputs at both analog interfaces of MC55/56.
2.65 V
Power down
MICP1
MICN1
Ri=50kΩ
to ADC
1 kΩ
1 kΩ
MICP2
33 µF
MICN2
1 kΩ
1 kΩ
Ri=2kΩ
Figure 17: Schematic of microphone inputs
MC55/56_hd_v04.00a
Page 57 of 108
24.08.2006