1. Physical layer protocol - Physical layer use UART to TTL communication interface, Baud rate is 9600, 8 data bits, 1 stop bit, no parity. 2. Application layer protocol - The application layer use the Modbus-RTU protocol to communicate. At present, it only supports function codes such as 0x03 (Read Holding Register), 0x04 (Read Input Register), 0x06 (Write Single Register), 0x41 (Calibration), 0x42 (Reset energy).etc. 0x41 function code is only for internal use (address can be only 0xF8), used for factory calibration and return to factory maintenance occasions, after the function code to increase 16-bit password, the default password is 0x3721 The address range of the slave is 0x01 - 0xF7. The address 0x00 is used as the broadcast address, the slave does not need to reply the master. The address 0xF8 is used as the general address, this address can be only used in single-slave environment and can be used for calibration etc.operation. Colour:White & Green Material:PC Package Contents: 1 * AC Single Phase Din Rail Meter 1 * USB cbale 1 * Connecting cable Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.