SPIM3的MOSI测试波形疑问

[chenzp531]

SPIM3配置，MOSI--P0.2，MISO--P0.28，SCK--P1.6，SS--P1.4，时钟频率125K，MODE0模式

如图，绿色为时钟，黄色为MOSI，在一个字节数据传输结束后，MOSI引脚引脚电平缓慢下降的状态，是否正常？期间更换其他引脚测试，均如此。

[SmallerPond]

Yes, perfectly normal:

[chenzp531]

那请问为什么会这样？

[SmallerPond]

I believe it is the small amount of pin capacitance coupled with the very high impedance you see at both ends of the connection.  You could probably put a very weak (100k?) pull down if it bothers you or you need it to drop faster, but the push-pull will pull it do it for you when it comes time to load up the next bit.

For reference: 5pF pin/line capacitance (low estimate since pad capacitance is already ~4pF) with 100MOhm impedance (also probably low estimate) would mean ~= 0.5ms time constant.  So this is about in line with what we see.

[chenzp531]

非常感谢！！！