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I'm trying to get my SmartCard reader to communicate with my phone's SIM card. I have a level shifter to drive 1.8V and 3.0V SIM cards, but the Wikipedia article specifies that there are also 5.0V SIM card. I just want to be sure that my SIM card is not a 5.0V one.

How can I determine the operating voltage of my SIM card? (I have access to a scope, and my SIM card is a Tesco Mobile one produced by Gemplus.)

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The ETSI standard ETSI TS 102 221 describes the procedure for switching (and thus finding the appropriate) supply voltage in section 6.2:

6.2 Supply voltage switching
The terminal shall initially activate the UICC with the lowest voltage class available. If no ATR is received, the UICC shall be deactivated and activated with the next higher class, if supported by the terminal. If an ATR is received at the first applied voltage class, the contents of the ATR shall be analysed by the terminal. If the operating class used by the terminal is not supported by the UICC, the terminal shall deactivate the UICC and activate it with a supply voltage class indicated by the UICC. If the ATR is corrupted, the terminal shall perform the procedure at least 3 times using the same operating class before rejecting the UICC. In case of 3 consecutive corrupted ATRs, the terminal may activate the UICC with the next higher class. The terminal is restricted not to use but the next higher class in the retrial attempt in this case.

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