GSM/GPRS Module Series
M85 Hardware Design
M85_Hardware_Design Confidential / Released 53 / 88
In order to enhance the reliability and availability of the SIM card in application. Please follow the below
criteria in the SIM circuit design:
Keep layout of SIM card as close as possible to the module. Assure the length of the trace as less
than 200mm as possible.
Keep SIM card signals away from RF and VBAT alignment.
Assure the ground between module and SIM cassette short and wide. Keep the width of ground no
less than 0.5mm to maintain the same electric potential. The decouple capacitor of SIM_VDD is less
than 1uF and must be near to SIM cassette.
To avoid cross talk between SIM_DATA and SIM_CLK. Keep them away with each other and shield
them with surrounded ground.
In order to offer good ESD protection, it is recommended to add a TVS diode array. For more
information of TVS diode, please visit http://www.onsemi.com/.The most important rule is to place the
ESD protection device close to the SIM card socket and make sure the nets being protected will go
through the ESD device first and then lead to module.
The 22Ω resistors should be connected in
series between the module and the SIM card so as to suppress the EMI spurious transmission and
enhance the ESD protection. Please to be noted that the SIM peripheral circuit should be close to the
SIM card socket.
Place the RF bypass capacitors (33pF) close to the SIM card on all signal lines for improving EMI.
3.10. SD Card Interface
The module provides SD card interface that supports many types of memory, such as Memory Stick,
SD/MCC card and T-Flash or Micro SD card. The following are the main features of SD card interface.
Only supports 1bit serial mode.
Not support the SPI mode for SD memory card.
Not support multiple SD memory cards.
Not support hot plug.
The data rate up to 48MHz in serial mode.
Up to 32GB maximum memory card capacity.
With the SD card interface features and reference circuit shown as below, you can easily design the SD
card application circuit to enhance the memory capacity of the module. The users can store some
high-capacity files to external memory card. Such as in the automotive application system, the module
can record and store the audio file to the SD card, and also can play the audio files in SD card.
