SIM voltage modes


Hello everybody,

Is there a way how I can determine what the voltage for a SIM card should be? Is there a command or can the SIM toolkit be used to determine whether the SIM card (connected the a Wavecom module) is 1.8, 3, or 5V card?

What is the minimum Version of core software to support 1.8V SIM cards? In the x50a AT Commands Interface Guide “SIM1V8ONLY” and “SIM1V8AND3V” are listed with FtrIDs for command AT+WFM, but when I do AT+WFM=2 on 640d09gg.Q2406B, I only get

+WFM: "SIM3AND5V",1,0

So I guess OpenAT 2.0 with the required core software is too old to support 1.8V cards, right?

What would a module do with SIM3AND5V enabled and an 1.8V card inserted? Is there any indication, would it reject the card, or could it be that the behaviour is not really predictable?

That brings me back to my first question… How do I know what kind of SIM it is???

Thanks in advance for any insights on that matter,



Here’s my view of your questions…

I have seen a Wavecom application example of a voltage switching circuit to switch between the 2 different voltage (3 and 5 volts) levels.

I guess its something similar for 1.8 volt.

It must depend on the settings in the module, I doupt its unpredictable? If you cant find anything in the documentation, try to ask the experts at Wavecom :slight_smile:

You can always call the owner of the SIM card (the network operator), they should know.



Thanks so much for your answer, Snoooze!

Best Regards,



since OpenAT 3.x 1.8V cards are supported.

The etsi spec GSM 11.18 describes the voltage switching as following:
The module shall start with the lowest voltage to read out the status word of the card.
If an answer was received the voltage is ok.
If no answer is received or an error response could not be handled at 1.8V, the voltage should be switched to 3V an the read out should start again.

But what does the wavecom module do?
The product specification describes the voltage switching with GPO_0 (for Q24xx).
Will the output of the sim_vcc always be 1.8V?
(Only in the case that at+wfm has activated “SIM1V8AND3V”)

Thanks for your help.



SIM Vcc output is always 3V.

If you want to manage 1.8V, you need to connect an external SIM level shifter (3V/1.8V) driven by GPO_0.

Then the module will internally toggle the GPO_0 output during the SIM card detection to switch to the good voltage.

An example of 1.8V/3V SIM interface implementation is available in the “Q2406 and Q2426 Customer Design Guidelines”.
You can find this document on the support web page :
Open AT Software & Wireless CPUs -> QUIK Q2406B -> INTEGRATION GUIDELINES


Hi Jay,

thanks for this information.

But what does the GPO_0 do when the application is using this port for other things?
Which path has the higher priority (the SIM-switch signal or the customer application)?



You cannot use both functionnalities at the same time.

If GPO_0 is reserved for SIM level shifter (see AT+WFM), then you cannot use this GPO for AT (AT+WIOM) or Open AT usage (an error is returned if you tried to use it).


Does the Q26 series then do the proper GSM switching method? The customer design guidelines for 1V8 and 3V SIM does not show any level shifting so I gather it has been moved into the module?