F/2F Card Reader Format & Wiring
Understanding F/2F (Frequency to Frequency) Protocol
F/2F (Frequency-to-Frequency) is an access control communication format used in legacy and specialized security systems. Unlike standard Wiegand or OSDP protocols, F/2F modulates credential data into frequency variations to transmit information between a card reader and the access control panel. It is commonly found in older security infrastructures and military or government applications where tamper resistance and offline functionality are critical.
F/2F was originally developed as an alternative to Wiegand and remains in use in proprietary security systems requiring compatibility with legacy hardware.
Why F/2F is Used
F/2F is still in operation today due to its:
- Legacy System Compatibility → Many older access control panels still rely on F/2F communication.
- Tamper Resistance → More difficult to spoof or intercept compared to Wiegand.
- Simple Implementation → Requires only a few signal lines for communication.
- No Data Encryption Requirements → Can operate in offline environments where encryption is not required.
However, F/2F lacks modern security features like encryption and bidirectional communication, making it vulnerable to interception or replay attacks.
How F/2F Works
F/2F operates by encoding binary data as frequency shifts rather than direct voltage pulses. Each bit of data is transmitted as a high or low frequency pulse, which the controller interprets as 1 or 0.
F/2F Data Transmission Process
- Card is Presented → The reader scans the card and extracts its credential data.
- Bit Encoding → The credential data is converted into a frequency-modulated signal.
- Transmission to Panel → The controller deciphers the frequency shifts and reconstructs the binary data.
- Validation & Access Decision → The panel checks the credentials against a stored database to permit or deny access.
This frequency-based approach allows F/2F to function reliably over long distances but is more susceptible to interference compared to modern encrypted protocols.
How F/2F is Wired
F/2F requires dedicated signal lines for data transmission, but wiring differs between supervised and unsupervised modes.
Unsupervised F/2F Wiring
| Wire Colour | Function |
|---|---|
| Red | +12V DC Power (Optional, if not powered separately) |
| Black | Ground (GND) |
| Green | Data (Frequency Modulated Output) |
| White | Clock Signal (Optional, depending on implementation) |
Unsupervised mode does not provide monitoring for reader tampering or communication failures, making it less secure.
Supervised F/2F Wiring
| Wire Colour | Function |
|---|---|
| Red | +12V DC Power (Optional) |
| Black | Ground (GND) |
| Green | Data (Frequency Modulated Output) |
| White | Clock Signal (Optional) |
| Blue | Reader Supervision (Tamper Detection) |
| Yellow | Door Status (For advanced monitoring) |
Supervised F/2F mode includes tamper detection and communication monitoring, improving security and reliability. If a tamper event is detected, the controller can trigger alarms or disable the compromised reader.
Supervised vs. Unsupervised F/2F
| Feature | Supervised F/2F | Unsupervised F/2F |
|---|---|---|
| Tamper Detection | ✅ Yes | ❌ No |
| Reader Monitoring | ✅ Yes | ❌ No |
| Security Level | 🔒 High | ⚠️ Low |
| Wiring Complexity | ⚠️ More Wires | ✅ Simpler Setup |
| Common Use Case | Government, High Security | Legacy Commercial Systems |
Supervised F/2F is the preferred option for modern implementations where tamper detection and fault monitoring are critical.
Security Considerations
Although F/2F provides some tamper resistance, it has several security weaknesses:
- No Encryption → Data is transmitted in an unencrypted format.
- Replay Attacks → Captured frequency signals can be replayed to gain unauthorized access.
- Limited Interoperability → Many modern access control panels do not support F/2F.
- Susceptible to Interference → Nearby electronic noise can disrupt frequency-based transmission.
To improve security, organizations should consider migrating to modern encrypted protocols such as OSDP or using multi-factor authentication to supplement F/2F systems.
Migration Considerations
Organizations using F/2F should evaluate upgrading to OSDP or encrypted Wiegand alternatives. The migration process typically involves:
- Identifying Existing Infrastructure → Determine if legacy F/2F readers can be replaced with modern smart card readers.
- Upgrading to Secure Protocols → Transition to OSDP with AES encryption for enhanced security.
- Deploying Multi-Technology Readers → Support both legacy F/2F and modern credentials for a phased migration.
- Implementing Tamper Detection & Monitoring → Ensure access control systems can detect and respond to reader tampering.
Multi-technology readers allow organizations to gradually phase out F/2F systems while maintaining compatibility with legacy infrastructure.
Final Thoughts
F/2F is a legacy access control protocol with limited security features, making it vulnerable to modern attack methods. Organizations should:
✅ Evaluate security risks associated with F/2F-based systems.
✅ Upgrade to modern encrypted credential formats such as OSDP.
✅ Use tamper detection and monitoring to enhance security.
By transitioning from F/2F to secure communication protocols, businesses can future-proof their access control infrastructure while reducing the risk of unauthorized access.