This page documents a Phoenix-style serial adapter that connects a SIM card or ISO 7816-compliant smart card to a PC’s 9-pin RS-232 port. The adapter complies with ISO/IEC 7816-3, which defines the electrical signals and transmission protocols for contact smart cards, and was widely used for GSM SIM card programming and pay-TV conditional-access card development during the late 1990s and early 2000s. A MAX232 integrated circuit shifts the RS-232 voltage levels (approximately ±10 V) to the TTL levels (0–5 V) required by the card’s I/O and RST lines, while a 3.579 MHz crystal supplies the card clock. The adapter draws its power from the card’s VCC line or from an optional external +5 V supply regulated by a 7805.
6 pin Simcard special connector to the sim card / smart card
9 pin D-SUB female connector to the computer’s cable
SIM interface
The adapter electronics receive their power supply from the smart-card reader device VCC line, or from an optional external +5 V supply. The card slot’s RST line is connected via one of the TTL-to-RS-232 drivers in the MAX232 to the DCD line (DB-9 pin 1), so that software and the reader can resynchronise readily in the event of a protocol error. The circuit can be tested with a terminal emulator and an external +5 V supply by disabling local echo: if every typed character still appears immediately on screen, the interface is functioning correctly. The adapter can also be used to allow a PC to monitor data traffic between a reader and a real card — connect the real card and the adapter in parallel with the reader and configure the PC software not to transmit.
Notes
- The DB-9 signal mapping used by this Phoenix-style adapter: DCD (pin 1) ← RST; RxD (pin 2) ← card I/O; TxD (pin 3) → card I/O via hex buffer.
- The MAX232 can be replaced by the low-power MAX220 or the LT1081 without circuit changes.
- A 74LS07N hex buffer and 74HC04N hex inverter buffer the TTL I/O signals between the MAX232 and the card connector.
- Every byte transmitted by the PC is also received back by the PC (loop-back inherent in ISO 7816-3 T=0 operation); host software must discard the echo of its own transmissions.
- The 6-pin SIM connector carries contacts C1 (VCC), C2 (RST), C3 (CLK), C5 (GND), and C7 (I/O) per ISO/IEC 7816-2; a sixth pin is a mechanical card-presence switch. Contacts C4, C6, and C8 are unused in modern SIM and smart cards.
- ISO/IEC 7816-3 specifies VCC at 4.75–5.25 V (Class A); the default card baud rate is 9 600 bps at a 3.5795 MHz clock (fi = 3.5795 MHz, Di = 1, elementary time unit = 372/fi).
- Two transmission protocols are defined: T=0 (asynchronous half-duplex character protocol) and T=1 (asynchronous half-duplex block protocol). The card signals which it supports in the ATR (Answer to Reset) sequence issued after power-on.
Signals
- VCC (C1) — card supply voltage, 4.75–5.25 V, max 200 mA; provided by the 7805 regulator or external supply.
- RST (C2) — reset line; driven high (≥ 4 V) by the MAX232 from DCD (DB-9 pin 1) to initiate or abort a session; low (≤ 0.6 V) holds the card in reset.
- CLK (C3) — clock input to the card; supplied by the 3.579 MHz crystal oscillator; initial ATR frequency must be 1–5 MHz with 45–55 % duty cycle.
- GND (C5) — ground reference.
- I/O (C7) — bidirectional serial data line; logic high ≥ 2 V, logic low ≤ 0.8 V, rise/fall time ≤ 1 µs; level-shifted via MAX232 between RS-232 RxD/TxD and TTL.
- Card presence — mechanical switch wired to the smart-card connector pins 9 and 10; signals card insertion to the host software.