GSM/GPRS Module Series
M85 Hardware Design
M85_Hardware_Design Confidential / Released 55 / 88
In SD card interface designing, in order to ensure good communication performance with SD card, the
following design principles should be complied with:
Keep all the SD card signals 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
10cm.
The SD_CLK, SD_DATA0 and SD_CMD trace should be routed together. Keep trace difference of
SD_DATA0, SD_CMD and SD_CLK to be less than 10mm.
In order to offer good ESD protection, it is recommended to add TVS on signals with the capacitance
less than 15pF.
Reserve external pull-up resistors for other data lines except the DATA0 signal.
The SD_CLK and SD_DATA0 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 15: Pin Definition of PCM Interface
8
DATA1
DATA1
9
DATA2
Pin Name
Pin No.
Description
PCM_IN
18
PCM data input
PCM_CLK
19
PCM clock output
PCM_OUT
20
PCM data output
PCM_SYNC
21
PCM frame synchronization output