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SPI modes
arjuna
#1 Posted : Saturday, October 20, 2012 6:57:43 PM(UTC)
Rank: Newbie

Joined: 10/20/2012(UTC)
Posts: 2

Can anyone tell me why there are four different modes in SPI? what is the advantage of giving such a flexibility? A single mode specifying that data is to be toggled at this instant (rising edge or falling edge of serial clock) and read on some other instant of same clock would have done.
Johan Dams
#2 Posted : Monday, October 22, 2012 5:28:36 AM(UTC)
Rank: Advanced Member

Joined: 9/16/2012(UTC)
Posts: 35

Hi.

As you mentioned in your post, the advantage is the flexibility you get. The SPI standard is pretty loose, and every device will implement it in its own way leading to the four different 'modes'. Combinations of polarity and phases lead to these modes since it was not specified in the standard which combination would be 'standard'. In the end though, because SPI is such a simple protocol, it doesn't really matter.


Johan.
arjuna
#3 Posted : Tuesday, October 23, 2012 3:27:24 AM(UTC)
Rank: Newbie

Joined: 10/20/2012(UTC)
Posts: 2

Thanks Johan. Got your point.
cdhmanning
#4 Posted : Wednesday, October 24, 2012 7:40:08 PM(UTC)
Rank: Newbie

Joined: 10/24/2012(UTC)
Posts: 2

SPI is not so much a spec that was designed to. It was originally an attempt to capture and codify some existing clocked serial protocols. ie. when the parts were released there was no standard to design to.

SPI was first defined as part of the SPI peripheral (??by Motorola??) which could operated in various modes to communicate with a variety of clocked serial devices that had already existed for some years.

That is very different to something like I2C or CAN where the spec predated devices.
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