SIM card connectors follow the ISO 7816 contact assignment: C1 = VCC (power), C2 = RST (reset), C3 = CLK (clock), C4 = AUX/NC, C5 = GND (ground), C6 = VPP/NC, C7 = I/O (data), C8 = NC. A 6-pin socket carries the essential contacts (C1, C2, C3, C5, C7 plus one auxiliary), an 8-pin socket exposes all eight, and a 2FF (full-size SIM) socket keeps the same C1-C8 electrical definition in a larger ID-1 form factor.

C1-C8 Pin Function Table (ISO 7816)

How Pin Counts Map to Real Sockets

The electrical contacts stay identical across socket sizes; what changes is how many contacts and switch pins the housing carries:

• 6-pin SIM connector: the most common mobile SIM socket. Carries VCC, RST, CLK, GND, I/O plus one auxiliary contact. See our 6-pin smart card connector with 2 switch pins (H 1.45mm) and 6-pin version with 2 detection switches (H 2.00mm).
• 8-pin SIM connector: full C1-C8 contact set, used in payment terminals and industrial readers where auxiliary contacts are required. See our 8-pin smart card connector with 2 switch pins (H 0.45mm).
• 2FF (full-size SIM) socket: ISO 7816 ID-1 card format; identical C1-C8 electrical mapping in a larger carrier, still common in industrial and automotive terminals.

Engineering Notes

• Card detection switches (present on our 6-pin and 8-pin sockets) report card insertion state to the host MCU without touching the ISO 7816 contacts.
• Push-push mechanism ejects the card with a second press; push type requires manual extraction.
• Always route CLK and I/O traces with controlled impedance and keep series resistors close to the socket for ESD robustness.