Embedded processor in ARM9 and μ Based on the C / OS-II operating system, the SD card, a storage medium with large capacity, small volume and high cost performance, is used to store the measurement data for a long time. FAT32 is cut and combined with the bottom reading and writing program of the SD card, so as to realize the embedded SD card file system, which can easily query the truck weighing data recorded by the SD card through the upper computer, Comprehensive analysis and backup. At the same time, this method provides a solution of nonvolatile memory for other data acquisition systems. The collected data will be recorded on the SD card in the format of standard file, which is convenient for the unified management of files. The system has the characteristics of strong real-time, high access rate, easy maintenance and easy transplantation.
1、 Hardware circuit
The processor of the system hardware development platform is s3c2440a. It is a 16 / 32-bit RISC microprocessor launched by Samsung, with ARM920T core. The main frequency is 400 MHz, up to 533 MHz. It has rich system peripheral controllers and a variety of communication interfaces. SD card supports SPI and SD communication modes. S3c2440a has SD card interface and supports SD bus mode. Therefore, instead of SPI mode like low-end ARM processor, SD bus mode is adopted, which can greatly improve the reading and writing speed of SD card. The interface circuit between s3c2440a and SD card reader is shown in Figure 1.
Figure 1 SD card interface circuit
Dat0 ~ dat3, CLK (clock line) and CMD (command line) of SD card are connected to sddata0 ~ sddata3, sdclk and sdcmd pins of s3c2440a respectively. SD card supports single line and wide bus data transmission. Wide bus data is transmitted 4 bits at a time, and the number is faster. Therefore, this design adopts wide bus mode.