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Altera_Forum
Honored Contributor
Honored Contributorwill Cyclone III work with unconected VCCA PLL ??
I actually made e board already and didn't connected thous VCCA PLL pins and now my board don't work (I can't program it and software all time is saying "can't access JTAG chain"
is that because of unconnected VCCA pins ? here is my DIY cyclone III board and I can't get it to work :( I have pull-up 10K ohm on CONF_DONE and nStatus + other Jtag pins are also conected like in Cyslone III handbook Figure 10–23. schematic. for programming I use self soldered Byteblaster II, programmer works correctly because I can program my old cyclone II board. https://www.alteraforum.com/forum/attachment.php?attachmentid=31815 Replies
Altera_ForumSuccess
my Cyclone III is alive I drilled hole to VCCA1 Pin and connected it to 2,6V supply. For supply I used single Diode HER105 which dropped voltage by 0,6V and I get 2,6V on VCCA1 Pin. So in my board all VCCIO banks are powered by 3,2V and i don't need additional 2,5V power supply I also left unconnected VCCA2 pin dos it have some impact on cyclone III ??? or I can leave it unconnected :)- Altera_Forum
thanks FvM
I will try to connect tomorrow this VCCA pin thorough silicon diode, by drilling hole down fpga VCCA pin, and then I will post my results :) - Altera_Forum
Hello,
you can supply 3.3V for VCCIO, but VCCA is fixed to 2,5V +/- 5 %. Altera however recommends to use 2.5V for configuration - for two reasons that shouldn't be mixed up. 1. There is an issue with power-up sequence, particularly with non-monotic voltage rise which can cause the configuration to fail. Please read the respective manual parts, but with a correct power supply, this issue shouldn't exist to my opinion. 2. The Cyclone III is apparently more sensitive to overvoltages than Cyclone II, thus Altera included multiple hints in the newer manual revision regarding potential damage due to overshooting configuration signals. I made some remarks in a recent Cyclone III configuration thread, that I don't repeat here. With goof design practice, e. g. having clamp diodes or on-board JTAG buffers, this shouldn't be an issue. But I see, that it's a good idea, to consider all 2.5V logic supply with new designs. The point with VCCA is that Altera introduced internal voltage regulators for PLL supply. Cyclone II users probably know why. Of course I can't know, if VCCA could operate with 3.3V, but it would be far out of allowed voltage range. I would use a series silicon diode from 3.3V as simple workaround during prototype evaluation and a small 2.5 V LDO later. This solution also worked with a customers design. Regards, Frank - Altera_Forum
It is relay sad :( because cyclone II was working without VCCA, thats why I omitted thous schematics in C3 handbook, but why need to use this 2.5V, why not 3.3 ???
does that mean that I need to set BANK1, BANK6 also to 2,5V ?? is there someone who tried to use 3,3V on VCCA and 1;6 BANKS ??? - Altera_Forum
Hello,
the simple answer is: cyclone iii won't work without vcca supply. As the manual clarifies, the 2.5v vcca supply, also different from Cyclone II must be present as well as the core supply to enable the configuration and boundary scan JTAG circuit. Regards, Frank
