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       Telit OEM GSM / GPRS / GPS modules   


Frequenty Asked Questions:

GSW1 Card

Q - Can the level shifter can be removed and links added so that people interfacing with embedded systems don’t have to convert to talk to it?

A - Yes. Remove the RS232 level shifter. You will have the option to install 0402 0-ohm resistors to override the level shifter. In the PDF. Remove U3 and add R22--R29 0 ohm  with soldering.

GSW1 Assembly Drawing 26KB

GR1 Card

Q - Is a RS232 <=> TTL interface chip  (Maxim MAX232 ) necessary from the PC's serial port to the GR1 module. I expect not, but better to ask.

A - Yes it is since there is no level conversion on the GR1 you will need to ensure that the logic levels to the GR1 are 3.3V. We recommend to connect the module to a USB to 3.3V serial cable (TTL-232R-3V3) from FTDI. Use the flow control pins also.

FTDI TTL-232R-3V3 Datasheet 508KB

Please be advised that if  the header has been connected on to the opposite side of the overlay if you use a ribbon cable to connect the module then every second ribbon cable wire will be odd for example, wire1=pin2, wire2=pin1, wire3=pin4, wire4=pin3 etc it is confusing I know but it can be remedied by using another crimp connector if you feel this is too confusing.  

1 – Provide 7V minimum to the module Pin1=Vin=wire2(ribbon cable) plus ground via Pin19=GND=wire20
2 – Provide Vin to enable pin Pin2=EN=wire1
3 – Make sure the GR1 module has a SIM and powers up. LED should be blinking fast and then slow once registered slow = one flash every 2 seconds.
4 – Connect RXD(pin4=wire3) to 3V3 TXD pin4 Orange
5 – Connect TXD(pin6=wire5) to 3V3 RXD pin5 Yellow
6 – Connect CTS(pin10=wire9) to 3V3 CTS pin2 Brown
7 – Connect RTS(pin12=wire11) to 3V3 RTS pin6 Green
8 – With the USB>RS232C connected test the serial port. Hyperterminal session should be able to communicate to the module.
9 – Make sure to use the latest revision of PythonWin. Contact us for a copy.
10 – Once you have PythonWin running you should be able to right click and download the Python script to the module.

Q - To which PIN of the 20 PIN connector on the GR1 board does the connection from the DB9 PC's serial connector PIN no. 5 (signal ground) go. I can clearly see the following:

DB9 (PC)       ------>   20 PIN molex (GR1)
PIN 1            (DCD)   PIN 13
PIN 2            (Rx)    PIN 4
PIN 3            (Tx)   PIN  6
PIN 4            (DTR) PIN 8
PIN 5               ?  ?
PIN 6            (DSR)  PIN 15
PIN 7            (RTS)  PIN 12
PIN 8            (CTS) PIN 10
PIN 9            (RING)    PIN 14

A – You will not want to connect the DB9 pins to the module, only the pins from the level conversion IC or cable. Be aware that if you intend to crimp an IDC header socket to plug into the DIL header on the module that the pins will be reversed. You will know what I mean once you plug the connector on and check with your multimeter.

Q - On the 20 PIN connector I see PIN 19 being the GND. Is this the connection PIN for the battery's or AC/DC power adaptor's  - (minus) pole? Or in other words to which PINs the power input (+ and -) needs to be connected?

A – I use this connection for signal ground and make another connection to the GND on the RF connector for improved GND but both are connected together so it doesn’t matter which one you use.

Q - Please explain the LDO Enable (PIN 2) and ON/OFF (PIN 16). How to use/connect? E.g how to connect a switch on/off button (to which PINs).

A – For the ON/OFF pin you need to refer to the Telit GE863-GPS Hardware User guide attached. For the EN pin refer to the MIC29510 data sheet page 4 VEN = VIN you only need to provide this voltage straight from Pin 1 the supply voltage to enable the regulator.

Q - The two GPIOs, are they 12V tolerant, or they are CMOS level (connected straight to the module)?

A - GPIO5 and GPIO6 do not offer any 12V level conversion so can only read 2.8V levels. All the available GPIO are at 2.8V levels including the serial port.

Q - What is the best mounting scheme for this module? I don't see any mounting holes from the picture.

A - There are two mounting holes on the GR1 it has been designed to be plugged down via the 10x2 dual row header and then to use clip on stand off or stand off with M3 screws.

Q -Does the Telit module start automatically when we apply power to the board or we still need some kind of circuit to start it up?

A - The GR1 is designed to allow you the option to start automatically at power up or by way of a momentary switch similar to turning on a mobile phone. If you choose to have it turn on and off by the application of 12V power then you must ignore J4 and  power the module from the main 10x2 header pin 1 and also connect pin 2 to pin 1 also thereby providing the enable to the regulator.

Q - Is the Telit module already preprogrammed with some scripts? and if so, are we able to read the source code or they are protected?

A - We have free Python scripts available which will run on the GR1 these can be tweaked according to your requirements. Please contact us with what you need and we can see what we have that can assist you.

Q - Can I download my own script in the module?

A - Yes once you have your script you only need to connect to the GR1 by way of using our FTDI USB to 3.3V serial cable (TTL-232R-3V3) to communicate, download and enable the script.

FTDI TTL-232R-3V3 Datasheet 508KB

Q - Can I see the schematic for the GR1?

A - Yes, please contact  us at with your company name, contact details, application and we can email you the schematic to you

Q - I connect 10V to the VIN, and use a 1K resistor to connect LDO to 10V. RESET is left open-circuit and is at about 2V. PWRMON is at about 3.5 - 4V. The RED LED is flashing at about 1 second when first powered up and then changes to short pulse every 3 seconds. But when pulse the ON/OFF pin via a transistor circuit the pin on the GR1 remains low. Is there something else I need to do?

A - It appears to me that you wish to be able to shut down the GR1 by grounding the ON/OFF pin. The ON/OFF pin to the GR1 has been designed to function in the reverse to the normal operation so when you apply voltage to the ON/OFF pin it will shut down the modem and the GR1 ON/OF circuit allows you top apply 3.8V up to the input supply rail voltage to the regulator like 14V. Below I have pasted the GR1 schematic refer to page 3.


Q - I am having difficulty getting CMUX to work properly with the GR1 or GE863-GPS.

A - There is a new function which has been added into the CMUX function refer to page 71 of the AT Command r4 document attached, I have pasted the change below. In order to circumvent this problem it is required now to assert AT#CMUXSCR=1 this will override the 5 seconds allowing CMUX to be enabled at power up, refer to page 399 of the AT Command r4 document.