Integration Guide

LEON-G100/G200 - System Integration Manual
GSM.G1-HW-09002-F3 Preliminary System description
Page 62 of 101
For debug purposes, include a test point at each I
2
S pin also if the digital audio interface is not used.
Refer to u-blox 2G GSM/GPRS AT Commands Manual [2], AT+UI2S command for possible combinations
of connection and settings.
1.10.2.1 PCM mode
In PCM mode I2S_TX and I2S_RX are respectively parallel to the analog front end I2S_RX and I2S_TX as
internal connections to the voice processing system (see Figure 40), so resources available for analog path can be
shared:
Digital filters and digital gains are available in both uplink and downlink direction. They can be configured
using AT commands; please refer to the u-blox 2G GSM/GPRS AT Commands Manual [2]
Ringer tone and service tone are mixed on the TX path when active (downlink)
The HF algorithm acts on I
2
S path
Main features of the I
2
S interface in PCM mode:
I
2
S runs in PCM - short alignment mode (configurable with 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 synchronism (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 are in 2’s complement
notation. MSB is transmitted first
When I2S_WA toggles high, first synchronization bit is always low. Second synchronism 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
1.10.2.2 Normal I
2
S mode
Normal I
2
S mode 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 the channel can be either high or low
I2S_TX data 16 bit words with 32 bit frame and 2, dual mono (the word can be written on 2 channels).
Data are in 2’s complement notation. MSB is transmitted first. The MSB is first transmitted; the bits change
on I2S_CLK rising or falling edge (configurable)
I2S_RX data are read on the I2S_CLK edge opposite to I2S_TX writing edge
I2S_CLK frequency depends by the number of bits and number of channels so is 16 x 2 x 8 kHz = 256 kHz
The modes are configurable through a specific AT command (refer to u-blox 2G GSM/GPRS AT Commands
Manual [2]) and the following parameters can be set:
I2S_TX word can be written while I2S_WA is high, low or both
MSB can be 1 bit delayed or non-delayed on I2S_WA edge
I2S_TX data can change on rising or falling edge of I2S_CLK signal
I2S_RX data read on the opposite front of I2S_CLK signal