User's Manual

LISA-U1/LISA-H1 series - System Integration Manual
3G.G2-HW-10002-2 Advance Information System description
Page 71 of 116
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 [2]):
 <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 parallel to the analog front end, 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 combinations of
connection and settings.
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: