The EM4200​ is a low-frequency (LF) 125 kHz read-only RFID chip​ manufactured by EM Microelectronic. It is widely used as a direct, high-performance replacement for the classic EM4100/4102 series in access control, animal ID, and industrial tagging.

1. Core Definition

The EM4200 is a CMOS integrated circuit​ designed for passive RF transponders. It is a factory-programmed, read-only​ device, meaning its unique ID (UID) is permanently written during manufacturing via laser ROM and cannot be rewritten​ in the field.

2. Key Technical Specifications

The chip includes an integrated voltage limiter and rectifier, allowing it to be powered entirely by the RF field from an external coil without needing external components.

3. Protocol Compatibility

• Backward Compatible: Fully compatible with EM4100, EM4102, EM4005, and EM4105​ protocols. Readers configured for these older chips can typically read EM4200 tags without modification.
• Standards: Supports ISO 11784/11785 (FDX-B)​ for animal identification.

4. Common Applications

• Access Control Systems: Office doors, gate entry (often in CR80 card or key fob format).
• Animal Identification: Livestock tracking (FDX-B standard).
• Industrial & Logistics: Asset tracking, process control.
• Anti-Counterfeiting: Product authentication tags.

5. Comparison with T5577

Unlike the T5577​ (which is read/write and configurable), the EM4200 is read-only. This makes it more secure against cloning in some contexts (as the ID is fixed at the factory) but less flexible for applications requiring data updates.

In summary, the EM4200 is a robust, low-cost solution for applications requiring a simple, permanent identification number with good read range and backward compatibility.