TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R28
Design-in
Page 112 of 164
2.7
Audio interface
2.7.1
Digital audio interface
☞
The I
2
S interface is not available on MPCI-L2 series modules.
2.7.1.1
Guidelines for digital audio circuit design
☞
The I
2
S interface is not supported by TOBY-L2 series modules “00”, “01”, “60”, TOBY-L201-02S and
TOBY-L220-62S product versions: the pins should not be driven by any external device.
I
2
S digital audio interface can be connected to an external digital audio device for voice applications.
Any external digital audio device compliant with the configuration of the digital audio interface of the
TOBY-L2 cellular module can be used, given that the external digital audio device must provide:
The slave role: opposite role of TOBY-L2 modules, which act as master only
The same mode and frame format: PCM / short synch mode or Normal I
2
S / long synch mode with
o
data in 2’s complement notation
o
MSB transmitted first
o
data word length = 16-bit (16 clock cycles)
o
frame length = synch signal period = 32-bit (32 clock cycles)
The same sample rate, i.e. synch signal frequency, configurable by AT+UI2S <I2S_sample_rate>
parameter
o
8 kHz
o
16 kHz
The same serial clock frequency:
o
32 x <I2S_sample_rate>
Compatible voltage levels (1.80 V typ.), otherwise it is recommended to connect the 1.8 V digital
audio interface of the module to the external 3.0 V (or similar) digital audio device by means of
appropriate unidirectional voltage translators (e.g. TI SN74AVC4T774 or SN74AVC2T245,
providing partial power down feature so that the digital audio device 3.0 V supply can be also
ramped up before V_INT 1.8 V supply), using the module V_INT output as 1.8 V supply for the
voltage translators on the module side
Support of the side-tone, which is not available in the internal audio processing system of
TOBY-L2 modules as summarized in
. The side-tone is a part of the user's speech on
uplink path that should be listened on downlink path by the user himself to have perception the
call is on.
For the appropriate selection of a compliant external digital audio device, see section
the +UI2S AT command description in the u-blox AT Commands Manual
regarding the capabilities and the possible settings of I
2
S digital audio interface of TOBY-L2 modules.
An appropriate specific application circuit has to be implemented and configured according to the
particular external digital audio device or audio codec used and according to the application
requirements.
Examples of manufacturers offering compatible audio codec parts are the following:
Maxim Integrated (as the MAX9860, MAX9867, MAX9880A audio codecs)
Texas Instruments / National Semiconductor
Cirrus Logic / Wolfson Microelectronics
Nuvoton Technology
Asahi Kasei Microdevices
Realtek Semiconductor
