Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
Hi experts,

In a new board design I have to build a generic IO PORT. This generic IO
port will be connected to an connector (20-pin header).

The output drive voltage will be LVCMOS18 for some applications and
LVTTL for some others applications.

My question is :
Did I need to specifiy LVCMOS18 and LVTTL in the .ucf file and create
two .bit files (one for LVCMOS18 and one for LVTTL) ?
OR could I only create one .bit and work with the VCCO only ?

Same questions for Coolrunner-II

Laurent Gauch

Hi Laurent,

Regarding CoolRunner-II, make sure that you configure the device for
LVTTL or LVCMOS18 accordingly.

You can either use the .ucf file to specify the constraint or use the
GUI to do it.

The LVTTL and LVCMOS18 settings affect the way that the CoolRunner-II
IOs are configured.  No real damage will occur if you set LVCMOS18 and
tie Vccio to 3.3V (or vice versa).  However, your rise/fall times and
drive strength will get affected if you have the wrong settings...

Hope that helps!

Amontec, Laurent Gauch wrote:
Quoted text here. Click to load it

Hi Mark,

Many thanks for your comments.

Is that the same for Spartan-IIE ?

My goal is to provide an new version of my Chameleon POD but using
USB2.0 and a colrunner or SPARTAN-IIE.
The first objective of this new Chameleon based USB2.0 will be to build
an JTAG interface accelarator.

Actually, JTAG can be 3.3V or 2.5V (will be 1.8V in future), so I ask me
if there are a sense  to do the voltage level converter directly with
the VCCO. The VCCO will be drived by the user board target.

What do you think, is that acceptable?

I will do some tests next week concerning rise/fall times and drive
strength when configuring the FPGA with LVTTL and driving the VCCO to
down 1.8V

Best regards,

Mark Ng wrote:

Quoted text here. Click to load it

Site Timeline