# Electrical reset to a SIM card

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?

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 Take a look at the answer here: electronics.stackexchange.com/questions/14259/… SIM cards adhere to the same (or a variation of) ISO standard as contact smart cards and the ATR procedure should be the same. @Curd could give an answer if he sees this. – Jon L Jul 10 '12 at 16:15 [service message] @JonL - the "@" in front of a user name is to notify him of your comment, but then he has to have commented here before as well, OP gets automatically notified. You can tell if he'll get notified if you get a hint when you start typing his name. – stevenvh Jul 11 '12 at 9:05 I guess you meant "an ATR is sent after an electrical reset by the card to the reader" (NOT "by the reader to to the card"). – Curd Jul 11 '12 at 9:16 @Curd: Thanks. Fixed. – Randomblue Jul 11 '12 at 10:14 @Curd, do you think you could post an answer similar to the one in the question that I linked in the first comment? OP is essentially asking how to trigger an ATR and you've pretty much already nailed it. – Jon L Jul 11 '12 at 16:19

## 2 Answers

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.

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There's an RST line in that pinout! Use that for reset.

I think that asserting the STOP signal (Active low) would most likely turn the VCC to SIM off as well.

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 The OP is asking how to trigger an ATR message. This involves manually driving the clock and reset line in a particular sequence – Jon L Jul 11 '12 at 16:25