Acr122 - Android / How To Extract The Uid

I try to integrate an ACR122 to my android app. I'm using the ANDROID Library (http://www.acs.com.hk/en/products/3/acr122u-usb-nfc-reader/) available from ACS. Everything work, I

Solution 1:

In case of Mifare card you need to send this APDU byte array to the card: (byte) 0xFF, (byte) 0xCA, (byte) 0x00, (byte) 0x00, (byte) 0x00 . I'm not sure about ACR122 API but probably you need to wrap this APDU into specific API method like transmit()

UPDATE

Sample code:

byte[] command = newbyte[] { (byte) 0xFF, (byte) 0xCA, (byte) 0x00, (byte) 0x00, (byte) 0x00 };
 byte[] response = newbyte[300];
 int responseLength;
 responseLength = reader.transmit(slotNum, command, command.length, response,response.length);
 System.out.println(new String(response));

Reader is com.acs.smartcard.Reader object and slotNum is a the slot number. I’m not sure how to find it because I don’t have ACR to test. But if you told that you was able to establish basic communication with reader probably you know slotNum.

Solution 2:

In order to prevent this error when trying to read the UID:

com.acs.smartcard.InvalidDeviceStateException: The current state is not equal to specific.

This should rather be:

int slotNum = 0;
byte[] payload = newbyte[] { (byte) 0xFF, (byte) 0xCA, (byte) 0x00, (byte) 0x00, (byte) 0x00 };
byte[] response = newbyte[7]; // 7 bytes + 90 00 (9 bytes)try {
    reader.power(slotNum, Reader.CARD_WARM_RESET);
    reader.setProtocol(slotNum, Reader.PROTOCOL_T0 | Reader.PROTOCOL_T1);
    reader.transmit(slotNum, payload, payload.length, response, response.length);
    logBuffer(response, response.length);
} catch (ReaderException e) {
    Log.e(LOG_TAG, e.getMessage(), e);
}