Cinterion
®
LTE Terminals Hardware Interface Description
3.6 GPIO Interface
47
ELSxT_HID_v04 2018-09-04
Confidential / Preliminary
Page 33 of 102
3.6.2 Digital Audio Interface (ELS61T-E2)
Four pins at the LTE Terminals‘ GPIO connector can be configured as digital audio interface
(DAI). The DAI can be used to connect audio devices capable of pulse code modulation (PCM).
The PCM functionality allows for the use of an external codec like the W681360.
The DAI interface supports a 256kHz, long frame synchronization master mode with the follow-
ing features:
• 16 Bit linear
• 8kHz sample rate / 125µs frame duration
• The most significant bit MSB is transferred first
• Data write at rising edge / data read at falling edge
• Common frame sync signal for transmit and receive
The following pins at the GPIO connector can be configured as DAI/PCM interface signals:
DOUT, DIN, FSC and BCLK (see also Table 14). The configuration is done by AT^SCFG com-
mand - see [1]. It is non-volatile and becomes active after a module restart. DAI/PCM and GPIO
functionalities for these lines are mutually exclusive. Table 15 describes the available DAI/PCM
lines at the digital audio interface
1
. For electrical details see Table 23.
Figure 12 shows the PCM timing for the master mode available with LTE Terminals.
Figure 12: Long frame PCM timing, 256kHz
Section 3.6.2.1 gives an example of how the DAI can be employed.
1. Note: For the DAI interface to operate, the directions of the LTE Terminals‘ GPIO level shifters must be
set according to the defined directions of the DAI signals. See Section 8.3.1.11 and Section 8.5 for more
information on how to change level shifter directions.
Table 15: Overview of DAI/PCM signals
Signal name Input/Output Description
DOUT (GPIO20) O PCM data from
LTE Terminals to external codec.
DIN (GPIO21) I PCM data from external codec to
LTE Terminals.
FSC (GPIO22) O
Frame synchronization signal to external codec:
Long frame (8kHz)
BCLK (GPIO23) O Bit clock to external codec: 256kHz
BCLK
DOUT
DIN
FSC
MSB
MSB
LSB
LSB
14 13
14
13
1
1
12
12
2
2
MSB
MSB
125 µs
11
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