JMY504 series are RFID reader/writer module with UART and IIC serial ports. JMY504 has various functions and supports multi ISO/IEC standard of contactless card; the cards from different suppliers. The RF protocol is complex. But the designer combined some frequent used command of RF card and then user could operate the cards with full function by sending simple command to the module through IIC or UART interface. And the module and antenna are separate design. The impedance between RF module and antenna was tuned by impedance analyzer. And then the module has excellent performance and stability. The module and antenna is separate design. 4 wires are linked the antenna and module. Normally the wire should be less than 200mm, or it will affect the module's performance and stability.