PCMCLK (bit clock) and PCMSYNC (frame synchronization) are both generated by the DSP within the wireless modem. The DSP within the wireless modem 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 5.10-1 below.

sample LSB justified

MSB

LSB

D15 D0

13-bit sample occupies these frame bits

Figure 5.10-1 Typical 16-bit PCM Voice Sample Word Format

Typical PCM data transfer is shown in the following figures.

SSPCLK

 

 

 

SSPFS

 

 

 

SSPDTM

MSB

LSB

Q

SSPDFM

Q MSB

LSB

 

Figure 5.10-2 PCM Frame format for a single transfer

SSPCLK

 

 

 

 

SSPFS

 

 

 

 

SSPDTM

LSB

MSB

LSB

MSB

SSPDFM

LSB

MSB

LSB

MSB

Frame n-1

Frame n

 

Frame n+1

Figure 5.10-3 PCM Frame format for a continuous transfer

The PCM interface has a Slave mode, however the allocated DSP buffer size limits the maximum data rate available. A separate Application Note describing slave mode implementation can be obtained from Sony Ericsson through Customer Support.

LZT 123 1834

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