1. Adopt PCIE to four-channel USB2.0 design, one USB2.0 is used for serial port expansion, and the other three USB2.0 are led out with 1.25mm 4Pin interface, which can expand the CM4 4G Mini module 2. Four serial ports are output through the USB2.0 high-speed interface, using two RS232 and two RS485 (with power isolation) designs. Two of the RS232 can be transformed into TTL/CMOS level UART and passed through the 2.54mm 3Pin pin. lead out 3. The RS232 baud rate can reach more than 230Kbps (the actual measurement of U0 and U3 docking can reach 1.2Mbps); 4. The RS485 baud rate can reach 500Kbps (the actual measurement of U1 and U2 docking can reach 1.5Mbps) 5.TTL/CMOS UART baud rate can reach 6Mbps; 6. There are four indicator lights in total, one of which is the power indicator light (works through the PCIE interface of Raspberry Pi 5), one is the ACT indicator light of the USB to serial port chip, and the other two are the transceiver indicator lights. 7. The board size is 56x85mm, the same as RPI5, with four fixing holes; 8. Reserve fixing holes for 4G modules and can stack 1-3 channels of 4G modules 9. Driver-free design, the default recognition in Raspberry Pi system and Ubuntu system is ttyACM*, ttyACM0 and 3 are RS232, and ttyACM1 and 2 are RS485: Due to different batches, the appearance, color and printed words of the product may vary, which will not affect the use. Colour:Blue Material:PCB Package Contents: 1 x Kit 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.