msel in multiple configuration schemes

I've successfully driven MSEL pins, on Cyclone IV, from a micro. Indeed we have a shipping product that does just that. This followed previous work doing the same thing on a proprietary Cyclone II development platform. Make sure you have control over nCONFIG too so that you can ensure the MSEL sttings are stable when nCONFIG is released - when the MSEL pins are sampled. Don't try and use fast POR - there's no point.

There is one large caveat with this - it's not supported. As you pointed out, the datasheet states they should be tied directly to GND of VCCA and specifically states "do not drive the msel pins with a microprocessor or another device". As Galfonz points out, jumpers/dip switches achieve this, the micro doesn't. Altera are unlikely to support you should not comply with the datasheet. However, with our shipping product we took the decision - following extensive testing that showed no failures - that the risk was low. 5 years and a large number of units later we have not seen any issues. My fingers remain crossed...

Cheers,

Alex

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Development boards use jumpers or dip switches.

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I've successfully driven MSEL pins, on Cyclone IV, from a micro. Indeed we have a shipping product that does just that. This followed previous work doing the same thing on a proprietary Cyclone II development platform. Make sure you have control over nCONFIG too so that you can ensure the MSEL sttings are stable when nCONFIG is released - when the MSEL pins are sampled. Don't try and use fast POR - there's no point.

There is one large caveat with this - it's not supported. As you pointed out, the datasheet states they should be tied directly to GND of VCCA and specifically states "do not drive the msel pins with a microprocessor or another device". As Galfonz points out, jumpers/dip switches achieve this, the micro doesn't. Altera are unlikely to support you should not comply with the datasheet. However, with our shipping product we took the decision - following extensive testing that showed no failures - that the risk was low. 5 years and a large number of units later we have not seen any issues. My fingers remain crossed...

Cheers,

Alex

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Thanks alot both of you!

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Thanks alot both of you!

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FYI, The Cyclone V databook has been updated to read:

Section 7-2:

MSEL Pin Settings

To select a configuration scheme, hardwire the MSEL pins to VCCPGM or GND without pull-up or pull-down resistors.

Note: Altera recommends connecting the MSEL pins directly to VCCPGM or GND. Driving the MSEL pins from a microprocessor or another controlling device may not guarantee the VIL or VIH of the MSEL pins. The VIL or VIH of the MSEL pins must be maintained throughout configuration stages.

https://www.altera.com/content/dam/altera-www/global/en_us/pdfs/literature/hb/cyclone-v/cv_5v2.pdf

I believe the main problem of a microprocessor driven MSEL pin is that it might not have the right state during POR.

There might be situations where you want to switch the configuration scheme e.g. by a processor. As it's unsupported, you need to find out yourself how it can be done reliably. Possibly you need to power-cycle the FPGA after switching MSEL.