SPI, triangular wave on data line between two bytes

[lpcware]

Content originally posted in LPCWare by emielzij on Thu Nov 27 03:49:10 MST 2014
I need to use spi to communicate with a device. A program has been made to send the decimal value '1'. It seems to be working fine, but I can't figure out why there is this triangluar shaped wave on the data line if the clock is inactive.

I will post my code if it is needed.

[IMG]http://i61.tinypic.com/2m4rj92.png[/IMG]

[lpcware]

Content originally posted in LPCWare by R2D2 on Thu Nov 27 05:05:49 MST 2014

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Quote: emielzij
...this triangluar shaped wave

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That's a little Christmas tree  :D Next week you'll see also little candles...

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Quote: emielzij
I will post my code if it is needed.

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I've no idea which MCU and which SPI device you are using...

Anyway: If SPI is inactive (=CS off) MISO isn't high or low, but often it's pulled up with a weak resistor (external or internal). So what you are seeing there is that your inactive MISO is slowly pulled up  :) 

If you increase the inactive time it will be high, sooner or later...

That's no problem at all, because MISO is inactive at that time. If MISO is active again (=CS on) the device will set MISO high or low again...

Note: You can add a pull-up or pull-down to avoid a floating MISO, but usually that's not necessary. Especially if the inactive signal is looking as stable as in your case...