移动设备（电话）和SIM卡间的通讯遵从ISO的T=0协议，电话向SIM卡发送APDU指款，SIM卡执行命令后返回一个返回报告（return code）。根据其内容或状态，电话再就APDU指示从卡中读取额外信息。-A link between the card and the external world starting with the ATR and ending with a subsequent reset or a deactivation of the card.

初始化SD卡 Reset: mrs r0, CPSR bic r0, r0, #0x1f orr r0, r0, #0xd3 msr CPSR_fc, r0 -init SD card Reset: mrs r0, CPSR bic r0, r0,#0x1f orr r0, r0,#0xd3 msr CPSR_fc, r0