GR4x to GR64 Migration Guide
2.2.5
PCM Audio
The GM/GR4x series implemented a PCM (digital) audio feature which permitted the
user to access the interface between the audio Codec and the DSP, which also allowed
additional DSP devices to be wired at this junction.
The GR64 baseband architecture does not lend itself to the same physical interface as
the predecessor hardware, since the digital audio is memory mapped to a parallel
data bus. However, the echo cancellation capability of GR64 is a vast improvement on
the predecessor series, and simply does not present the same challenges.
The legacy variant GR64 will allow legacy application PCBs, wired so that the
respective PCM uplink and downlink paths are connected, to remain unchanged.
However, any external circuitry connected to these pins will not function. Instead, the
advanced echo and noise canceling properties of the GR64 will compensate for the
loss of such circuitry.
A PCM audio interface is still available in a standard 4-pin implementation for the
integrated SIM variant GR64, using a Texas Instruments SSI implementation.
Fig A: GR4x implementation showing the PCM UL & DL paths wired together
Migration Guide
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GR4x to GR64
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