EM4100 & T5577
Smart Cards & RFID · 6 specs
Direct Answer
EM4100 and T5577 represent the foundational low-frequency (LF, 125 kHz) RFID transponder ecosystem. The EM4100 (EM-Marin) is a factory-programmed, 64-bit read-only identity chip, while the Atmel/Microchip T5577 is a rewritable EEPROM transponder used to emulate and clone various 125 kHz LF protocols.
Source: EM Microelectronic / Microchip Technology Inc. · Last reviewed Aug 28, 2026
Specs
| Frequency Bands | 100 to 150 kHz (125 kHz nominal) |
| EM4100 Memory Structure | 64 bits (9 header bits, 40 customer/ID bits, 15 parity/stop bits) |
| T5577 Memory Capacity | 330 bits (10 blocks of 33 bits EEPROM) |
| Modulation Schemes Supported | Manchester, Biphase, FSK, PSK |
| Data Rates (Typical) | RF/64, RF/32, RF/16 clock divisors |
| Cryptographic Protection | None (Plaintext transmission) |
EM4100 Protocol Structure
The EM4100 protocol continuously broadcasts its 64-bit payload whenever energized by an interrogator coil. The payload comprises 9 leading logic-1 header bits, followed by 10 groups of 4 data bits each paired with an even parity bit, 4 column parity bits, and a final logic-0 stop bit. Because the serial number is broadcast in plaintext with zero authentication, any receiver within magnetic coupling range can read the ID.
T5577 Dual-Mode Cloning Capabilities
The Microchip T5577 transponder contains configurable analog front-end registers. By programming its Block 0 configuration bitmask, the T5577 can perfectly mimic the modulation, bit rate, and payload structure of EM4100, HID Prox, Indala, Motorola, or AWID credentials, making it the industry-standard chip for key fob duplication.