TCM4400E Datasheet, PDF (35/64 Pages) Texas Instruments – GSM/DCS BASEBAND AND VOICE A/D AND D/A RF INTERFACE CIRCUIT

TCM4400E
GSM/DCS BASEBAND AND VOICE A/D
AND D/A RF INTERFACE CIRCUIT
SLWS082A – JULY 1999 – REVISED MARCH 2000
PRINCIPLES OF OPERATION
DAI interface
This digital audio interface (DAI) consists of four terminals: SSRST, SSCLK, SSDR, and SSDX. It is compatible
with the digital audio interface described in the GSM recommendation 11.10. This interface is designed to offer
minimum CPU overhead during audio tests and speech transcoding tests and to minimize the extra hardware
and the number of external terminals of the mobile system (MS). With this interface the DSP does not have to
deal with rate adaptation. In normal operation the DSP works with an 8-kHz sampling rate with a 16-bit word
format and frame synchronization, but the DAI interface works with an 8-kHz sampling rate with a 13-bit word
format without frame synchronization. The DSP (or the MCU) does not have real time constraints with SSRST,
since the reset of the internal transmitters is done automatically.
The DAI is controlled with four internal bits of VBCTL3 register:
DAION: When 0, the DAI block is put in low power. When 1, the DAI block is active.
VDAI:
This bit controls the start of the clock SSCLK. The falling edges of SSRST automatically resets the
VDAI.
DAIMD 0/1: These two bits are used to switch the internal data path of the three types of DAI tests:
Tests of acoustic performance of the uplink/downlink voice path
Tests of speech decoder/DTX functions (downlink path)
Tests of speech encoder/DTX functions (uplink path)
In order to correctly execute these tests, the bits DAION/VULON/VDLON must be reset before starting the DAI
test. In the case of acoustic tests the following must be set with the sequence: DAION and VDAI, then VULON,
and finally VDLON. In case of vocoder tests, when the speech samples are ready to be exchanged with the
system simulator, the bits DAION and VDAI must be set at the same time.
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