Pcm Data Format - Wavecom GR64 GSM/GPRS Integrator's Manual

5.10.1 PCM Data Format

The PCM digital audio interface for GR64 is based upon the Texas Instruments SSI
standard. The SSP interface can be programmed for data frame sizes between 4 to 16
bits. The clock rate is fixed to 128kHz.
PCMCLK (bit clock) and PCMSYNC (frame synchronization) are both generated by the
DSP within the Wireless CPU. The DSP within the Wireless CPU in this instance is the
master for all external PCM, so clocks and data from external devices must be
synchronized to it.
For standard GSM voice a 13-Bit PCM data word is embedded in a 16-bit word frame,
as shown in Figure 20 below.
MSB MSB
D15 D15
Figure 20: 13-bit GSM voice embedded in 16-bit PCM Frame
Typical PCM data transfer is shown in the following figures.
SSPCLK SSPCLK
SSPFS SSPFS
SSPDTM SSPDTM
SSPDFM SSPDFM
Figure 21: PCM Frame format for a single transfer
Q in Figure 21 above indicates unknown or invalid data content which should be
disregarded.
GR64 Integrators Manual
Page: 57/104
13-bit sample occupies these frame bits 13-bit sample occupies these frame bits
MSB MSB
Q Q
MSB MSB
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sample LSB justified sample LSB justified
LSB LSB
LSB LSB Q Q
LSB LSB
D0 D0