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SPI boot AN76405 is it possible to connect MOSI and MISO also to a FPGA I/O as well as to the SPI flash?
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SPI boot AN76405 is it possible to connect MOSI and MISO also to a FPGA I/O as well as to the SPI flash?

Lumpi6 posted on 12 Feb 2013 3:36 PM PST
Top Contributor
183 Forum Posts

 Hi,

I had read the DVK description as well as the AN76405. Both documents describe that the MISO and MOSI lines in SPI boot mode should not be connected to a pull up resistor. I do not know if it will work when I have connect those pins also to a FPGA I/O? Can anybody tell me a specifically description of the behaviour of MOSI and MISO lines.

thanks, 

lumpi

Re: SPI boot AN76405 is it possible to connect MOSI and MISO also to a FPGA I/O as well as to the SPI flash?

RSKV posted on 13 Feb 2013 11:36 PM PST
Cypress Employee
655 Forum Posts

Hi Lumpi,

You should be able to connect SPI lines to different slaves with out any issue. In your case, they are FPGA and SPI flash.

CS or SS (Slave Select) decides the device that FX3 wants to communicate.

Are you seeing any issue regarding this use case.

Please let me know.

Thanks,

sai krishna.

Re: SPI boot AN76405 is it possible to connect MOSI and MISO also to a FPGA I/O as well as to the SPI flash?

AssemblyRequired posted on 13 Feb 2013 05:32 AM PST
Top Contributor
37 Forum Posts

It's critical to the boot process that there not be a pull-up on MISO. Some FPGAs have internal pull-ups, so you may need to add a strong pull-down in order to boot properly.

Steve

Re: SPI boot AN76405 is it possible to connect MOSI and MISO also to a FPGA I/O as well as to the SPI flash?

AssemblyRequired posted on 13 Feb 2013 05:45 AM PST
Top Contributor
37 Forum Posts

Clarification: floating MISO is not good either, if your boot flash tri-states that signal.


Steve 



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