Isolation resistors necessary for SPI devices with opposite phase/polarity?

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Are isolation resistors necessary for SPI devices on the same bus as the ISP if the device uses CPOL = 1 and CPHA = 1?

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I don't think I really understand what you are asking but anyway: smiley

 

The ISP header must be connected directly to the SPI pins

 

Resistors are likely to slow down communications, not necessary if each slave device has a CS pin and you use a pullup or pulldown on the pin depending on polarity.

 

Unless you have the chip select enabled on more than 1 devise (VERY BAD IDEA) you can do anything you want with the polarity as only the device enabled talks to the SPI.

 

Make sure you change the setting of the SPI depending on clock and phase polarity expected by the slave device you are addressing.

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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ckalas wrote:

Are isolation resistors necessary for SPI devices on the same bus as the ISP if the device uses CPOL = 1 and CPHA = 1?

I'd think not. When the slave select (SS) is false the slave device shall ignore the clock and data lines and NOT assert a logic level on MISO.