LISA-U1 series - System Integration Manual
3G.G2-HW-10002-3
Preliminary
System description
Page 75 of 125
If the I
2
S digital audio pins are not used, they can be left unconnected on the application board.
The I
2
S interface can be can be used in two modes:
PCM mode
Normal I
2
S mode
To select the I
2
S digital audio interface the AT+USPM command parameters must assume these values (for more
details please refer to
u-blox AT Commands Manual
<main_uplink>: “I2S input line”
<main_downlink>: “I2S output line”
Parameters of digital path can be configured and saved as the normal analog paths, using appropriate path
parameter as described in the
u-blox AT Commands Manual
[2], +USGC, +UMGC, +USTN AT command. Analog
gain parameters of microphone and speakers are unused when digital path is selected.
I2S_TX
and
I2S_RX
are respectively connected in parallel to the analog microphone and speaker connections, so
resources available for analog path can be shared:
Digital filters and digital gains are available in both uplink and downlink direction. Configure using AT
commands
Ringer tone and service tone are mixed on the TX path when active (downlink)
The HF algorithm acts on I
2
S path
Refer to the
u-blox AT Commands Manual
[2]: AT+UI2S command for possible settings of I
2
S interface.
1.11.2.1
I
2
S interface - PCM mode
Main features of the I
2
S interface in PCM mode:
I
2
S runs in PCM - short alignment mode (configurable by AT commands)
Module functions as I
2
S master (
I2S_CLK
and
I2S_WA
signals generated by the module)
I2S_WA
signal always runs at 8 kHz
I2S_WA
toggles high for 1 or 2 CLK cycles of synchronization (configurable), then toggles low for 16 CLK
cycles of sample width. Frame length can be 1 + 16 = 17 bits or 2 + 16 = 18 bits
I2S_CLK
frequency depends on frame length. Can be 17 x 8 kHz = 136 kHz or 18 x 8 kHz = 144 kHz
I2S_TX
,
I2S_RX
data are 16 bit words with 8 kHz sampling rate, mono. Data is in 2’s complement notation.
MSB is transmitted first
When
I2S_WA
toggles high, the first synchronization bit is always low. Second synchronization bit (present
only in case of 2 bit long
I2S_WA
configuration) is MSB of the transmitted word (MSB is transmitted twice
in this case)
I2S_TX
changes on
I2S_CLK
rising edge,
I2S_RX
changes on
I2S_CLK
falling edge
1.11.2.2
I
2
S interface - Normal I
2
S mode
Normal I
2
S supports:
16 bits word
Mono interface
8 kHz frequency
Main features of I
2
S interface in normal I
2
S mode:
I2S_WA
signal always runs at 8 kHz and synchronizes 2 channels (timeslots on WA high, WA low)
