Will onboard SPI slave devices affect ICSP programming given both use same pins?

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lightaiyee
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Posted by lightaiyee: Thu. Aug 6, 2015 - 07:02 AM
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I would like to use ICSP programming on Atmega328 and Atmega1281. However, the circuit board also uses a SPI slave device. Since ICSP and the SPI slave device both use MISO, MOSI and SCK, will ICSP programming be affected by the SPI slave device due to conflicts? If yes, what are some hardware changes needed to get ICSP programming working?

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AVR Microcontrollers, megaAVR and tinyAVR
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Bronze Markdavid.prentice
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Posted by david.prentice: Thu. Aug 6, 2015 - 07:27 AM
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There will be no problem with genuine SPI slaves if they are powered.

 

For ICSP to work,  each Slave's /CS pin must be controlled by an external pull-up resistor.    This ensures that the Slave is de-selected when the AVR is not running (i.e. when being programmed)

 

For theusch:   In the event that you have an unusual SPI Slave with an active-high CS pin,  you use an external pull-down resistor.

 

David.

Last Edited: Thu. Aug 6, 2015 - 07:30 AM
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awneil
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Posted by awneil: Thu. Aug 6, 2015 - 07:49 AM (Reply to #2)
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david.prentice wrote:
genuine SPI slaves

ie, SPI slaves in which de-asserting CS does prevent the device from doing anything on the bus.

 

each Slave's /CS pin must be controlled

and not just tied "permanently active" ... 

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