1 ETU = (F / D) * (1 / f)
Where：
ETU: In asynchronous half-duplex communication, the nominal duration required to transmit one data bit (bit), with the unit being seconds (s).
f: The external clock signal frequency provided by the interface device (such as a mobile phone or card reader) to the SIM card via the CLK pin, with the unit being Hertz (Hz).
D: An integer or fraction used to adjust the number of clock cycles occupied per bit. It essentially acts as a "speed multiplier" coefficient.
Standard SIM card pinout for mini, micro, and nano variants (ISO/IEC 7816). Includes pin functions: VCC (power), GND, I/O (data), CLOCK, RESET, and reserved pins. Essential for embedded design, mobile hardware development, and SIM interface troubleshooting.
Connector at the card
| Pin | Description |
|---|---|
| 1 | [VCC] +5V or 3.3V DC power supply input Provides operating voltage to the SIM chip. |
| 2 | [RESET] Card reset, used to reset the card's communications (optional) Sends a reset signal to restart communication protocol. |
| 3 | [CLOCK] Card clock Synchronizes data transfer between the mobile device and SIM card. |
| 4 | [RESERVED] AUX1, optionally used for USB interfaces and other uses Not used in standard GSM/UMTS/LTE SIMs; reserved for future or specialized applications. |
| 5 | [GND] Ground Common ground reference for all signals. |
| 6 | [VPP] +21V DC programming voltage input (optional) Used during manufacturing to program the SIM chip; not active in normal operation. |
| 7 | [I/O] Input or Output for serial data (half-duplex) Bidirectional data line for exchanging information between the phone and SIM. |
| 8 | [RESERVED] AUX2, optionally used for USB interfaces and other uses Reserved for future use or special applications such as smart card emulation. |
This guide is designed for technical specialists and learners in embedded electronics and telecommunications, including:
Embedded Hardware Engineers: Designing cellular IoT devices, smart meters, and automotive telematics systems (T-Box).
Firmware & Driver Developers: Writing smart card ISO/IEC 7816 communication drivers and handling Answer-to-Reset (ATR) parsing.
Repair Technicians & Forensic Investigators: Repairing mobile device SIM readers or extracting SIM data using smart card interface tools.
Engineering Students & Researchers: Studying ISO/IEC 7816 smart card protocols, hardware security, and embedded interface design.
This reference serves key engineering functions during hardware design and troubleshooting:
Custom PCB Design & Socket Layout: Correctly routing traces from cellular modules (e.g., Quectel, SIMCom) to SIM card holders, ensuring decoupling capacitors (100 nF) are placed near VCC (C1).
Logic Analyzer Signal Debugging: Hooking test probes to C2 (RST), C3 (CLK), and C7 (I/O) to analyze the Answer to Reset (ATR) sequence during module boot-up.
ESD & Interference Protection: Selecting transient voltage suppressor (TVS) diode arrays matched to the pin layout to prevent electrostatic discharge damage on user-accessible SIM trays.
Operating Voltage Classes: Modern SIM cards support Class B (3 V) and Class C (1.8 V), with ultra-low power devices using Class D (1.23 V). Connecting a 1.8 V-only card to a 5V legacy supply without level shifting can permanently damage the chip.
6-Pin Socket Omission: Standard 6-pin SIM connectors omit C4 and C8. Because basic cellular functionality (GSM/LTE/5G authentication) only requires power (VCC), ground (GND), reset (RST), clock (CLK), and data (I/O), C4 and C8 are omitted unless advanced NFC or USB features are implemented.VCC
This reference tool provides pinout mappings, contact functions, electrical signals, and mechanical form factor specifications according to the ISO/IEC 7816-2 and ETSI TS 102 221 standards. It supports standard 8-contact and 6-contact Subscriber Identity Module (SIM) form factors, including Standard SIM (1FF), Mini-SIM (2FF), Micro-SIM (3FF), and Nano-SIM (4FF).
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