I have a SIM card reader connected to an ARM, and I'm trying to get the SIM to send an Answer To Reset (ATR) and to get the reader to capture it.
As I understand, an ATR is sent after an "electrical reset" by the card to the reader. Now in my design, VDD to connected to 3.3V so I cannot use that pin to make the electrical reset. The only other pin I see can that be used for that purpose is the STOP pin. However, the datasheet specifies that the STOP was not designed for the electrical reset:
With the STOP pin a low current shutdown mode can be activated making
the battery life longer
How should I make an electrical reset to the pin to get an ATR?
Best Answer
After applying power to the SIM card you must first supply a clock to the clk pin. Use something in the 3-3.5MHz range. Then pull the reset pin of the SIM card low for about 100ms, drive the reset pin high again, and listen to the I/O line for the ATR. It should come in at your clock frequency / 372 or something like that. The baud should be somewhere just under the 9600 range. I recommend scoping the line to find the exact rate.