User Manual

LARA-R2 series - System Integration Manual
UBX-16010573 - R02 Objective Specification Design-in
Page 114 of 148
2.7 Audio interface
Audio is not supported by LARA-R204 module “02” product version.
2.7.1 Digital audio interface
2.7.1.1 Guidelines for digital audio circuit design
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 LARA-R2
series cellular module can be used, given that the external digital audio device must provide:
 The opposite role: slave or master role, as LARA-R2 series modules may act as master or slave
 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:
 17-bit or 18-bit in PCM / short alignment mode (16 + 1 or 16 + 2 clock cycles, with the Word
Alignment / Synchronization signal set high for 1 clock cycle or 2 clock cycles)
 32-bit in Normal I
2
S mode / long alignment mode (16 x 2 clock cycles)
 The same sample rate, i.e. synch signal frequency, configurable by AT+UI2S <I2S_sample_rate> parameter
o 8 kHz
o 11.025 kHz
o 12 kHz
o 16 kHz
o 22.05 kHz
o 24 kHz
o 32 kHz
o 44.1 kHz
o 48 kHz
 The same serial clock frequency:
o 17 x <I2S_sample_rate> or 18 x <I2S_sample_rate> in PCM / short alignment mode, or
o 16 x 2 x <I2S_sample_rate> in Normal I
2
S mode / long alignment mode
 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
For the appropriate selection of a compliant external digital audio device, see section 1.10.1 and see the +UI2S
AT command description in the u-blox AT Commands Manual [2] for further details regarding the capabilities
and the possible settings of I
2
S digital audio interface of LARA-R2 series 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.