First, to do a show, the green line is SPI_DIN,the red is PG6, the blue is PA2, the yellow is trigger.When we make a data acquisition system, we use the stm32f405zgt6 as mcu and ADS131E08 as analog-digital converter. In the project, we use the SPI2 to transmit data via DMA1, use FSMC to control the external SRAM. During the practice, we found that there is a abnormal point after of , which is not constant. Using the leCroy oscilloscope catch the abnormal CS signal liker the blue line. After that, configure the PG6(GPIOG,GPIO_Pin_6), which have the same configuration compared to PA2(GPIOA,GPIO_Pin_2). But from the figure we can find the two signals are distinct. The red is normal which is we want to be and the blue one is not.