Chapter 6 – Application Considerations
Multi-Tech Systems, Inc. MMCModem GPRS Developer’s Guide (S000445D)
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Chapter 6 – Application Considerations
Hardware and RF
•
Ground plane: Multi-Tech recommends having a common ground plane for analog, digital and RF
grounds.
•
Length of the SIM interface lines (15 cm maximum)
•
Bias of the microphone inputs must be properly adjusted when using audio connectors (mic +
speaker) 1.
•
EMC protection on audio input/output (filters against 900 MHz)
•
ESD protection on serial link,
•
Possible spurious emission radiated by the application to the RF receiver in the receiver band
Firmware Upgrade
The MMCModem firmware is stored in flash memory and can easily be upgraded. Contact the factory
for details.
Changing the GPRS Quad Band
The MMCModem GPRS-F4 wireless modem supports quad band (850/1900/900/1800 MHz). In
reality, it operates like two dual-band modems. In other words, it can be configured for 850/1900 or
900/1800 MHz. Note: It does not auto-seek the local area frequency.
Build Options
The GPRS-F4 wireless modems can be ordered with a default band of 850/1900 MHz or 900/1800
MHz.
•
850/1900 MHz
–
The wireless modem defaulting to 850/1900 MHz is identified with
F4
in the
product ordering number. Example:
MTMMC-G-F4
. This build option is most commonly used
in North American.
•
900/1800 MHz
–
The wireless modem defaulting to 900/1800 MHz is identified with
F4-ED
in
the product ordering number. Example:
MTMMC-G-F4-ED
. This build option is most
commonly used in Europe.
Changing the GPRS Band
If for any reason, such as changing the geographical area in which you use your modem, you want to
change the band, you can accomplish it by using the
+WMBS
AT Command.
Steps for Changing the GPRS Band
You must use a terminal application such as HyperTerminal in order to enter the AT Command.
1.
To open HyperTerminal, click
Start
. Then select
Programs
>
Accessories >
Communications
. Then click
HyperTerminal
.
2.
When the command window opens, type
AT+WMBS=<Band><Param>
.
Press
Enter
.
For
<Band>
. Enter the option you desire:
4
= Dual-band mode 850/1900MHz
5
= Dual-band mode 900/1800MHz
For
<Param>
, enter the option you desire:
0
= The modem will have to be reset to start on the specified band(s). This is the default.
1
= The modem restarts immediately on the specified band(s).
Example: AT+WMBS=4,0. Press Enter.
