Integration Manual

LISA-U2 series - System Integration Manual
UBX-13001118 - R25 System description Page 95 of 182
1.11.3 I
2
S interface application circuits
LISA-U2 I
2
S digital audio interfaces 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
cellular module can be used, given that the external digital audio device must provide:
 The opposite role: slave or master for LISA-U2 modules that may act as master or slave
 The same mode and frame format: PCM / short alignment or Normal I
2
S mode / long alignment
mode with
o data in 2’s complement notation
o MSB transmitted first
o word length = 16-bit
o frame length = 17-bit or 18-bit in PCM / short alignment mode (16 + 1 or 16 + 2 clock cycles, with
Word Alignment / Synchronization signal set high for 1 clock cycle or 2 clock cycles), or
o frame length = 32-bit in Normal I
2
S mode / long alignment mode (16 x 2 clock cycles)
 The same sample rate and serial clock frequency: as the clock frequency depends on the frame
length and the sample rate, the clock frequency can be
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. Texas Instruments SN74AVC4T774 or
SN74AVC2T245), using the module V_INT output as a 1.8 V supply for the voltage translators on
the module side
For the appropriate selection of a compliant external digital audio device, 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 the I
2
S digital audio interface of LISA-U2 series modules.
Figure 49 shows an application circuit with a generic digital audio device.
43
I2S_CLK
41
I2S_WA
I
2
S Clock
I
2
S Word Alignment
LISA-U2 series
42
I2S_TXD
44
I2S_RXD
I
2
S Data Input
I
2
S Data Output
GND
GND
1.8 V digital
audio device
Figure 49: I
2
S interface application circuit with a generic digital audio device
Because, in general, any external digital audio device compliant to the configuration of the digital
audio interface of the cellular module can be used with LISA-U2 series modules, an appropriate
specific application circuit must be implemented and configured according to the particular external
digital audio device or audio codec used and according to the application requirements.