Configuration I/O voltage

[Altera_Forum]

I am attempting to locate 2.5V LVDS differential signals into Bank 3A of a Cyclone V device - this being the Bank that also contains the Configuration pins. 

  In Quartus II - Device Assignments / Device and Pin options.. / Configuration I am able to specify "Active Serialx4" scheme and select configuration device "EPCQ128".  Now, there are two more Options :   1) Configuration device I/O voltage - with selection of "Auto" or 3.3V     .... I'd like to know what the "Auto" setting does here - do I NEED to set it to 3.3V or does Auto do this for me (as its an Altera Device that is selected).   But more importantly :    2) (Tick box) - " Force VCCIO to be compatible with configuration I/O voltage "  for which the description comes up :  "Forces the VCCIO voltage of the configuration pins to be the same as the configuration device I/O voltage"    - now what I'm trying to understand is what this box does, and why I would choose NOT TO tick it.....    - If I leave it unticked, my design passes the I/O Assignment analysis phase. (= Job done ??)   But if I tick it, I get messages :   ! 169213 Configuration voltage level of 3.3V is enforced on the I/O Bank 3A. The VCCIO of the I/O Bank is set to 3.3V   followed by errors for the LVDS pins :   ! 169235 I/O bank 3A cannot select VCCIO of 2.5V which is required for pin ("pin_name") with I/O standard LVDS    This behaviour implies that leaving the tick box unticked allows me to have the configuration pins within Bank 3A operating at 3.3V I/O and the LVDS pins within Bank 3A operating at 2.5V I/O......(which is what I would like to achieve)  - Is this a correct assumption ?

[Altera_Forum]

Did you determine if it is possible to have bank 3A at 2.5V? I am facing the same issue. I want to use AS config mode and also need almost all available LVDS inputs on the device. The documentation indicates that Vccpgm must be at 3.0 or 3.3V for AS mode, but from what I can see makes no mention of bank 3A Vccio requirements. If bank 3A Vccio must be at 3.3V, I cannot place all the LVDS inputs.

[Altera_Forum]

--- Quote Start ---  Did you determine if it is possible to have bank 3A at 2.5V? I am facing the same issue. I want to use AS config mode and also need almost all available LVDS inputs on the device. The documentation indicates that Vccpgm must be at 3.0 or 3.3V for AS mode, but from what I can see makes no mention of bank 3A Vccio requirements. If bank 3A Vccio must be at 3.3V, I cannot place all the LVDS inputs.  --- Quote End ---    You should take a look at the information on the pins that are powered  up by VccPGM in http://www.altera.com/literature/hb/cyclone-v/cv_52007.pdf page 7. Various of the signal pins power up using VccPGM and then when configured, switch to using VCCIO for the Bank that they are in. You might have to provide some form of isolation for the lower voltage devices when the pins are operating at the higher of vccPGM and VCCIO - but this will not be very neat.

[EdJ]

I have this same question now (7 years later).  Did it work out for you the way you wanted?  (I've seen too many mistakes with configuration circuits to not ask this question.)

I am using LVDS inputs in bank 3A of the Cyclone V E.  I want to use the ASx4 configuration scheme (EPCQ128) and be able to program the config device through JTAG using the Serial Flash Loader.  It seems straightforward based on the documentation:  

VCCPGM

"The configuration input buffers do not have to share power lines with the regular I/O buffers in Cyclone V

devices.

The operating voltage for the configuration input pin is independent of the I/O banks power supply,

VCCIO, during configuration. Therefore, Cyclone V devices do not require configuration voltage

constraints on VCCIO."

We are using VCCPGM = +3.3V which is required for the ASx4 configuration scheme, while VCCIO3A = +2.5V (required by LVDS).

The JTAG power and pull up should be VCCPD3A = VCCIO3A = +2.5V.

Let me know if there is any problems hiding here.

Thanks,

Ed