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  Technical FAQs

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General

A Development Starter Kit(DSK) is available for development purposes.

GPRS refers to General Packet Radio Service. GPRS is charged based on the amount of data transferred rather than by airtime. This service is ideal for mobile professionals with a need to maintain an “always-on” Internet connection without incurring hefty GSM airtime charges. For example, once your emails have been downloaded or sent, there are no further charges—even if you are still connected to the Internet - as no data is being transferred. 

AT commands, also called Hayes AT commands, are based on the Hayes Modem de facto standard, ATTENTION Commands for modems. They are used to communicate with module or modem. These commands modify module or modem's behaviour or instruct the modem to do something specific, such as dialling a telephone number. The "AT" refers to getting the ATtention of your modem.

The time it takes to execute an AT Command may vary, you should receive a response within 60 seconds.

By default,  the network will keep a PDP Context open for  1-4 hours, typically, without data transfer, unless  operator stipulates otherwise.

Gateway GPRS Support Node (GGSN) generates the IP address and passes it to the module along with QOS parameters to the module if dynamic IP addressing is used.

In GPRS, a customer pays to the service provider not for the number of hours the subscriber is attached to the GPRS network, but for the amount of data transferred. Since it is difficult to calculate the amount of data packets transferred, different network operators actually implement different charging techniques. For example, some network operators charge fixed monthly/yearly amount for the usage of network service.
There is no AT command that will display the billing amount for a GPRS connection.

There is no way to determine the loss of GPRS coverage. You must instead verify coverage via GSM registration (AT+CREG?).  This means that if you check GPRS (AT+CGATT?) it may show connected (0,5) even though it is not.   This specifies loss of coverage only for GSM not GPRS.
When a device is in a no coverage area, you will see “AT+CREG?” return “+CREG: 0,2” or “+CREG: 0,3” for GSM registration; meaning the device is searching or has been rejected on the current network or has limited service, respectively."
 

 

GSM/GPRS Module Specific

All modules/modems supports all four frequency bands in the GSM network. They are (GSM850, GSM900, DCS1800, PCS1900)

The minimum voltage to power on module is 3.4V. It is advised to supply 3.6V to ensure best performance during operation

When establishing GPRS connection, a burst current of up to 2A will  be drawn.
Thereafter, normal transmission current will vary from 200mA to 400mA.

The recommended specifications when choosing an antenna are as follows:
- 50ohm matching impedance
- Gain of 0dbi
- VSWR < 2

Yes. TR-900 and TR-900C support auto PowerOn.

We support the data formats as follows:
- 8 data 2 stop
- 8 data 1 parity 1 stop
- 8 data 1 stop
- 7 data 2 stop
- 7 data 1 parity 1 stop
- 7 data 1 stop
with supported Odd, Even, Mark, Space, None

Currently, the GPRS class cannot be changed using a AT command. This is a customerised feature. Please refer to your account manager.

Following ways can be used to reduce the time for receiving a "NO CARRIER" response after terminating the GPRS call:
- The DTR pin can be changed to logical low. This can be done using the external application or by using a GPIO (connected to DTR pin) to change the logic level of DTR pin.
- The CMUX protocol can be enabled and a "STATUS" packet to indicate the lowering of DTR signal can be sent to the module. This will close the GPRS session immediately. This method can be used if the external application does not have the DTR signal.

The “AT+CGDCONT” command can be used to specify 2 different PDP Contexts. However out of the 2 PDP Contexts the TR-900 supports only one PDP Context to be active at any point of time. Hence even by using the multiplexing option, it is not possible to make two GPRS connections at the same time.

There are many buffers in the module for GPRS data transfer. It is not possible to give the exact size for each of these buffers as it is not the number of bytes which is considered, but the number of packets. These packets can have different sizes.

Modems have network selection set to automatic by default (AT+COPS=0). The modem control script does not need to issue the AT+COPS command to avail of automatic network selection.
A modem with manual network selection will perform GSM registration only if the specified
network is available.
Make sure your application gives the modem enough time to register. If you use a timer to
determine GSM registration success, make sure that you allow at least five minutes.

If the LED doesn't blink, check the following.
-Antenna, if it is properly connected
-SIM, check if SIM is inserted properly, also ensure SIM cover is close properly.
-Check if there is a PIN for the SIM

Yes , you can do that using "AT&W" which saves the desired baudrate to the non-volatile memory of the module.

Steps:
1) AT+IPR=
2) Change communicating speed between module and host to
3) AT&W

Yes, you can do that. However, you need to do either of the following:

1) Set and save AT+IFC=0,0 (no flow control), OR
2) Tie RTS and CTS on the module side to GND to imitate that these lines are always active
2.1 ) Connect DTR line (GPIO-3 ) to GND if not required for use

Yes. You can perform a download using our Firmware Programmer Tool for firmware upgrade purposes.

For firmware upgrade,  there are two alternatives:
- For USB approach, application board need to provide for access to USB signals and VBAT.
- For UART approach, application board need to provide for access to UART_TX  UART_RX,  1V8 and VBAT.

It is acceptable for an application to reboot the modem in case of GSM registration failure or in case of GPRS Attach failure due to transient reasons or due to no network available, but no more frequently than once every minute, and no more than 4 times in succession.

Our module supports voltage from the range 3.2V to 4.5V. It is recommended to connect a voltage regulator to bring it down to nominal operating voltage of 3.6V.

A reset is initiated by either pulling RESET or PWON low. Refer to Technical Specification document for design note.

You can issue the command AT+CCED=0,1 to obtain the main cell information.

Yes. It synchonizes to the speed of MCU or application  on initial start-up or after reset. 

AT+CMEE is the AT Command that enables the modem to report errors. It is important that
error reporting is enabled as it allows for the application to take action based on the error result.
AT+CMEE=1   Enable numeric error codes (the error response includes a value to indicate the detail of the error in question. For example, error value 10 means no SIM inserted.
AT+CMEE=2   Enable verbose error code (the error response includes a text string describing the error situation. For example “SIM not inserted.
Refer to AT Command Guide for more details.

Yes, please refer to AT Command for more info.

Yes, TR-900 module supports SIM Detect.

To send special characters in SMS, SMS PDU message format will have to be used.
You can set it to PDU mode by setting AT+CMGF=0.
To convert SMS to PDU format, free softwares on the internet can be used.