Design of usbhost related modules in the most popu

Design of usbhost related module in vehicle traveling data recorder

this paper introduces the design of related module to realize USB host function in vehicle traveling data recorder based on single chip microcomputer and USB host interface chip. This module well realizes the fast transfer of large amount of data from single chip microcomputer to USB flash disk in vehicle traveling data recorder LH m R002 m 0650 1v0 represents LH series, m18x1.5 thread, 02 meter cable, metric system, 650mm stroke, 0 ⑴ 0vdc output speed, and the pump station is equipped with cooler transmission

overall design of USB host related module

the USB host related module in the vehicle traveling data recorder is composed of MCU, USB host interface, flash, ferroelectric memory (FRAM), real-time clock and power management, and its functional block diagram is shown in Figure 1. When the vehicle traveling data recorder works, the single chip microcomputer picks up various information of the vehicle driving status through the front-end interface circuit, including vehicle speed, engine speed and various vehicle switch signals. The vehicle traveling data recorder takes the real-time clock as the benchmark 3 Orthopedic implant preparation technology stores vehicle information into fram and flash by category. When it is necessary to obtain the vehicle record status information from the vehicle traveling data recorder, the user inserts the USB flash drive, and the MCU automatically recognizes the USB flash drive and loads the driver. When the device enumeration and bulk are completed_ After the only transmission protocol, the single chip microcomputer can transmit the status information recorded in the vehicle traveling data recorder to the USB flash disk in the form of files. This paper focuses on the hardware design of power module, USB host module and data storage module

considering the complex working conditions of the car and the cost performance of the recorder, the single chip microcomputer is at least an industrial product. Due to the USB host structure, flash and ram should be large enough so that the system resources are sufficient. In addition, considering the cost and development cycle, it is more advantageous to choose 51 series for single chip microcomputer. Considering the above factors, single chip microcomputer chooses at89c51rd2 to expand ram; At present, there are more USB device chips in the market, while host is less. Two points should be considered when selecting USB host interface chip: first, it must be easy to connect with 51 single chip microcomputer in hardware, and second, the software development cannot be too difficult, so sl811hst is selected. For the data storage body, it must meet the requirements that the storage time is 15 years and the storage capacity is at least 360 hours of effective data. The number of ordinary data flash erasure is 1million times, which cannot meet the requirements of the recorder for frequent erasure of data. While the number of ferroelectric erasure is infinite, but the price of large capacity fram is very high. Taking these two points into consideration, the storage body adopts the combination of small capacity fram and flash, This not only meets the requirements of the recorder, but also has a relatively low cost

hardware design of power module

the most fundamental reason for electromagnetic interference of automotive electronic products is the di/dt generated in its working process. The power module is designed to work normally under these interference sources, and its hardware circuit is shown in Figure 2

at the power input, the function of diode VD1 (IN4007) is to prevent reverse connection, so that even if the power supply is reversed, the electronic equipment will not be damaged; VD2 (a36a) is a transient suppression diode, which can absorb the high-voltage pulse voltage and prevent the damage of electronic equipment caused by the high-voltage pulse generated during the operation of high-power devices; L1 and L2 are low inductance magnetic strips, which can effectively lose the energy of interference components and improve the power performance; F1 and F2 are self resetting diodes to prevent damage to other devices caused by power short circuit when devices in electronic equipment are damaged. The three terminal regulator 7812 (N2) provides 12V voltage to meet the needs of the pickup circuit of the front-end input interface. At the same time, it provides input to the three terminal regulator 7808 (N1), and N1 provides 8V voltage to meet the needs of mileage output and speed output. The switching regulator lm2576 (N3) provides 5V output, and the maximum output current is 3a, which meets the needs of the recorder with printer. Wrd24b05 (N4) is a DC-DC converter, which isolates the power supply of automobile and electronic equipment, making the equipment power supply stable and reliable. The forward voltage regulator spx1117 (N5) provides 3.3V voltage for sl811hst and memory. The transistor 8550 at the front end of N6 controls the input of N6, and N6 supplies power to IC card, which requires controllable power supply

usb host module hardware design

in the USB host module of vehicle traveling data recorder, the single chip microcomputer adopts at89c51rd2, and the USB host interface chip adopts sl811hst. The hardware circuit of the module is shown in Figure 3. Sl811hst provides parallel port bus data protocol and control lines CS, RD, WR, intrq and A0. Sl811hst and at89c51rd2 can be connected by using the read-write signal lines Rd, WR, and control lines A0 and INT1 of the single chip microcomputer, Among them, 8 data lines exchange data with at89c51rd2 under the control of the control line. USB host includes USB device enumeration protocol and bulk_ Only transmission protocol and fat file structure. The ram resources of at89c51rd2 are insufficient. Therefore, the system expands 32KB SRAM, which occupies a low 32KB address. In order to ensure the reliability of the sl811hst, the logic circuit is extended with hc00, so the sl811hst has two addresses 0x8000 and 0x8001 on the production material. In addition, the electrical characteristics of USB bus require that 22 ~ 44 Ω resistors must be connected in series before the USB transceiver, and the positions of pull-up resistors and pull-down resistors must be configured according to different USB device transmission speeds (full speed or low speed)

when CS and RD are valid, if A0 is high, this is to read the current address or register data; if A0 is low, then read the current address or register address. When CS and WR are valid, if A0 is high, this is to write the current address or register data. If A0 is low, then write the current address or register address

usb host device identification process is as follows: when sl811hst is connected to USB device, an interrupt will be generated. At89c51rd2 enters the enumeration process after receiving the interrupt. There is still some work to be done from the USB device plug-in interface to the customer driver can use the device. This section can be called the device identification process, also known as the enumeration process. The enumeration process is a necessary process for all USB devices before use. Before using, the USB host needs to know whether it is a low-speed device or a full speed device. It needs to know some characteristics and capabilities of the device in order to load the corresponding driver. After the USB host is configured with the USB device, the bulk is identified by the information provided by the descriptor_ Only mass storage device, and then enter bulk_ Only transmission mode. In this mode, all data between USB and the device is transmitted through bulk_ In and bulk_ Out, and no longer transmit any data through the control endpoint. In this transmission mode, there are three data types transmitted between USB and devices, CBW, CSW and ordinary data. CBW（Command Block Wra