LISA-U2 series - System integration manual
UBX-13001118 - R27
System description
Page 95 of 183
C1-Public
1.11.3
I2S interface application circuits
LISA-U2 I2S 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: local device or host for LISA-U2 modules that may act as host or local device
•
The same mode and frame format: PCM / short alignment or Normal I2S mode / long alignment
mode with
o
data in 2’s complem
ent 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 I2S 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 I2S 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
for further details regarding the capabilities and
the possible settings of the I2S digital audio interface of LISA-U2 series modules.
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: I2S 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.
