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Tom Schouten tom at zwizwa.beOn 07/26/2013 05:05 PM, Kevin Redon wrote: > Excerpts from Tom Schouten's message of 2013-07-26 22:55:32 +0200: >> Hi folks, >> >> Seems not all phones use 3V signaling if the PHONE-side VCC pin is tied >> to 3V. >> This one insists on 1.8V : BLU SAMBA JR PLUS > how does the phone behave? if the at91 doesn't respond, the phone goes through the following power/reset sequence, about 1 second apart: 1.8V 3V 3V 1.8V the at91 seems to mostly interpret the 1.8V serial line correctly, so the phone just starts talking at 1.8V until this eventually goes wrong. > >> Is this trick of tying VCC to 3V standard behavior? > no, it is not standard. It just works (most of the time). > And it should not damage the SIM nor the phone. > >> For future version of the board, it might be interesting to tie the VCC >> pin to an ADC input, to detect different voltage levels so the firmware >> can wait until phone decides to use 3V. >> > this will be done in the next board > good ( next to some GPIOs maybe ;)