Proximity Card Frequencies & Standards Glossary

What are the two main RFID frequencies for access cards?

Access credentials almost always operate in one of two bands. Low frequency (LF) is centered on 125 kHz and powers classic proximity cards such as HID Prox, Indala, AWID and EM-based cards. LF read range is short, the data is usually a small, open ID number, and the physics make LF tags forgiving of metal and liquids. The closely related 134.2 kHz band is the global standard for animal identification under ISO 11784/11785, not building access.

High frequency (HF) is 13.56 MHz and carries the modern smart-card families: MIFARE, DESFire, iCLASS, Seos, NFC and FeliCa. HF supports far more memory, mutual authentication and strong encryption, which is why secure sites and hotels have moved to it. A reader tuned for one band is deaf to the other, so a 125 kHz prox card and a 13.56 MHz smart card are never interchangeable even though they look identical.

• 125 kHz LF: legacy prox, short range, usually an open, unencrypted ID
• 134.2 kHz LF: animal ID only (ISO 11784/11785 FDX-B), not building access
• 13.56 MHz HF: smart cards, more memory, optional strong encryption
• 860-960 MHz UHF: long-range tags used by a few modern access platforms

Which ISO/IEC standards define 13.56 MHz contactless cards?

Three ISO/IEC standards do most of the work at 13.56 MHz. ISO/IEC 14443 covers proximity cards read at roughly up to 10 cm and defines two signaling variants, Type A and Type B, that differ in modulation and anti-collision but share the band. MIFARE, DESFire and many bank and transit cards are 14443 Type A; some national ID and payment cards are Type B. ISO/IEC 15693 covers vicinity cards read at a longer range, up to about a meter, and is used by NXP iCODE and many library, laundry and hotel tags.

ISO/IEC 18000-3 is an air-interface standard for 13.56 MHz item-management tags; Mode 1 is built on the 15693 vicinity protocol and Mode 3 aligns with other HF item tags, so you will see 18000-3 cited alongside iCODE. These standards define how a card and reader talk at the radio layer; they do not by themselves define the security of the data, which is why a 14443 Type A card can be an open MIFARE Classic or a strongly encrypted DESFire EV3.

What are NFC Forum tag types and NTAG21x?

NFC (Near Field Communication) is a 13.56 MHz technology built on top of the same ISO/IEC 14443 and 15693 foundations, with the NFC Forum defining five tag types for interoperability. Types 1 and 2 are simple read/write memory tags, Type 2 being the most common; Types 3, 4 and 5 add capacity and features, with Type 4 mapping onto 14443 Type A/B smart cards and Type 5 onto 15693 vicinity tags.

NTAG21x (NTAG213, 215 and 216) is NXP's widely used NFC Forum Type 2 chip family, differing mainly in user memory. These chips appear in marketing tags, product authentication and some simple access fobs. They carry a unique serial number and optional small data, but a plain NTAG is not an encrypted credential, so it is not a substitute for a DESFire or Seos card on a secured system.

What do Wiegand, facility code, CSN and UID mean?

Several data terms come up constantly when matching a card. Wiegand, in this context, is a data format, not the legacy wiring: it describes how a credential's bits split into a facility code and a card number with parity, with the open 26-bit H10301 being the textbook example. The facility code (also called site or company code) identifies the building or organization, and most controllers admit only cards whose facility code matches the door's configured value.

CSN (Card Serial Number) and UID (Unique Identifier) refer to the chip's factory-set serial number that every contactless card transmits. The crucial point is that the CSN is read openly by any compatible reader and is not a secret key; it is simply the data an open system already keys on. For those open formats we encode a compatible credential that presents the exact data your readers already accept. Secured smart credentials authenticate encrypted application data instead; for those we supply compatible blanks that your own system enrols with its keys, exactly as it would credentials ordered through the OEM channel.

• Wiegand format: how the bits split into facility code, card number and parity
• Facility / site / company code: identifies the building or organization
• CSN / UID: the chip's open, factory serial number, not a secret key
• FSK / ASK / PSK: how the card modulates its data onto the carrier

What is the difference between FSK, ASK and PSK modulation?

Modulation is how a tag encodes its bits onto the radio carrier, and on 125 kHz LF the modulation scheme is part of what makes one prox brand incompatible with another. ASK (Amplitude-Shift Keying) varies the signal strength and is used by EM4100 and most generic prox. FSK (Frequency-Shift Keying) shifts between two frequencies and is the scheme HID Prox uses. PSK (Phase-Shift Keying) shifts the carrier phase and is used by Indala and some Idteck cards.

Two 125 kHz cards can be physically identical yet unreadable to each other's readers purely because one uses FSK and the other PSK. A multi-emulation programmable blank such as a T5577 can be configured for the right modulation, bit rate and encoding so it reads identically to the original on an open format. Secured HF credentials do not hinge on modulation in the same way; their protection is cryptographic, so for those we supply compatible blanks your own system enrols.