GSM/GPRS Module
M85 Hardware Design
M85_Hardware_Design Confidential / Released 59 / 92
In order to ensure good performance for communication with SD card, the rules below should be followed.
Keep all the SD card lines far away from VBAT power and RF trace.
Route all SD card signals as short as possible. Ensure the length of every trace does not exceed
100mm.
The SD_CLK and SD_DATA and SD_CMD trace should be routed together. Keep trace difference of
SD_DATA, SD_CMD and SD_CLK to be less than 10mm.
In order to ensure good ESD protection, it is recommended to add TVS on signal pins with the
capacitance less than 15pF.
Reserve external pull-up resistor for other data lines except the DATA0 signal.
The SD_CLK and SD_DATA line must be shielded by ground in order to improve EMI.
3.11. PCM Interface
M85 supports PCM interface. It is used for digital audio transmission between the module and the device.
This interface is composed of PCM_CLK, PCM_SYNC, PCM_IN and PCM_OUT signal lines.
Pulse-code modulation (PCM) is a converter that changes the consecutive analog audio signal to discrete
digital signal. The whole procedure of Pulse-code modulation contains sampling, quantizing and
encoding.
Table 18: Pin Definition of PCM Interface
3.11.1. Configuration
M85 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.
11
NC
Pin NO.
Pin Name
Description
18
PCM_IN
PCM data input
19
PCM_CLK
PCM clock output
20
PCM_OUT
PCM data output
21
PCM_SYNC
PCM frame synchronization output
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