Design of data transmission interface circuit for a car driving recorder

The USB interface has the characteristics of fast data transmission speed, simple connection, and good compatibility. The national standard for automobile driving recorders takes into account the popularity of the RS232 interface and the advancement of the USB interface, and stipulates the simultaneous use of these two interfaces to achieve data communication. In the design of USB data transmission, the PDIUSBD12 chip is used as the USB controller. PDIUSBD12 fully complies with the USB version 1.1 specification; at the same time, it also complies with the classification specifications of most devices; it is also suitable for many peripherals, such as printers, scanners, external storage devices and digital cameras, etc. It allows systems currently using SCSI to Reduce costs immediately.

The microcontroller directly reads and writes the flash disk, which can realize plug-in mass storage for portable devices or embedded systems. The core of this technology is USB-HOST technology, the implementation of FAT file system specifications, the implementation of mass storage protocols and the implementation of USB batch transfer methods. There are many protocols involved and the technical difficulty is very high. In the design scheme shown in Figure 3, the USB interface chip uses Cypress's USB-HOST interface chip SL811, which supports the USB1.1 protocol, has low price, outstanding performance and high reliability. The file system adopts FAT format and is compatible with Windows 98 and Windows 2000/XP. It can be successfully accessed by flash drives produced by most manufacturers.

In order to improve the reliability and EMI characteristics of the circuit, the following rules should be paid attention to during the circuit board design and wiring process: add decoupling capacitors between the power supply and ground wires; try to widen the width of the power supply and ground wires, preferably the ground wires. The line is wider than the power line; the signal line is laid on the electrical (ground) layer; in a large area of ​​ground (electrical), the pins of commonly used components are connected to it, and the handling of the pins needs to be comprehensively considered; the wiring design is completed Finally, it is necessary to check whether the wiring design complies with the rules set by the designer, and it is also necessary to confirm whether the rules set meet the needs of the printed board production process.