Forum Discussion
Honored ContributorCyclone II + Quickswitch = 5V PCI? How Reliable?
I am trying to build a 5V PCI card with a Cyclone II and i am probably going to follow AN330 instructions using quickswitchs. I am not worried about not being fullly PCI compliant but what worries me is if 3.3V will be enough to be considered as a high level for the PCI host (Computer). How reliable will be that approach? Is there any other solution other than using a real PCI bridge?
Sugestions are apreciated. Thank you! Luis5 Replies
Altera_ForumThank you, i will take that in consideration but in my final designe it is suposed to work with a 3.3V Bus so that wont be a real problem. If it does works with a godd reliability on a 5V PCI bus i will be very satisfied..
- Altera_Forum--- Quote Start --- Do you know the 5V PCI spec? It's TTL based on TTL levels, Voh,min is 2.4V. --- Quote End --- It's minimum 2.4 to compensate for imperfect output and input stages (on real TTL) and loses from propagation, it gives you a safe windows if you are driving with 4.5-5V . If you are driving it with 3.3V the loses in the signal line may be enough to give you occasional hiccups or intermittent bugs. In principle it should work, but I would test it thoroughly before using it in anything serious.
- Altera_Forum
As AN330 explains, there are limitations regarding PCI impedance matching. It can cause voltage levels outside the PCI levels, if the bus connection length is large.
- Altera_Forum
Very well thought out. Thank you for objective response.
I did forget of checking TTL specs... Thank you - Altera_Forum
Do you know the 5V PCI spec? It's TTL based on TTL levels, Voh,min is 2.4V.
