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Why delay is different?

Question asked by li kai on Mar 20, 2017
Latest reply on Mar 22, 2017 by Clive One

signal-waves of PA2, PG6, SPI2_SDI,trigger

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 some interval of time, 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.