Configuration; Timing - Quectel M35 User Manual

3.9.1. Configuration

M35 module supports 13-bit line code PCM format. The sample rate is 8 KHz, and the clock source is 256
KHz, and the module can only act as master mode. The PCM interface supports both long and short
synchronization simultaneously. Furthermore, it only supports MSB first. For detailed information, please
refer to the table below.
Table 14: Configuration
PCM
Line Interface Format
Data Length
Sample Rate
PCM Clock/Synchronization Source
PCM Synchronization Rate
PCM Clock Rate
PCM Synchronization Format
PCM Data Ordering
Zero Padding
Sign Extension

3.9.2. Timing

The sample rate of the PCM interface is 8 KHz and the clock source is 256 KHz, so every frame contains
32 bits data, since M35 supports 16 bits line code PCM format, the left 16 bits are invalid. The following
diagram shows the timing of different combinations. The synchronization length in long synchronization
format can be programmed by firmware from one bit to eight bits. In the Sign extension mode, the high
three bits of 16 bits are sign extension, and in the Zero padding mode, the low three bits of 16 bits are
zero padding.
Under zero padding mode, you can configure the PCM input and output volume by executing
―AT+QPCMVOL‖ command. For more details, please refer to Chapter 3.9.4.
M35_User_Manual
Linear
Linear: 13 bits
8KHz
PCM master mode: clock and synchronization is
generated by module
8KHz
PCM master mode: 256 KHz (line)
Long/short synchronization
MSB first
Yes
Yes
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