Answers Database
Virtex: What are the differences between Vref(R) and Vref(r) in the package drawings
Record #6110
Product Family: Hardware
Product Line: Virtex
Product Part: Virtex General Hardware
Problem Title:
Virtex: What are the differences between Vref(R) and Vref(r) in the package drawings
Problem Description:
Keyward: Virtex, Vref, R, r, Package
Urgency: standard
Problem Description:
Virtex datesheet uses R and r to represent Vref pins in the package drawings.
What are the differences between R and r?
Solution 1:
If an IO_STANDARD does not require to use Vref, the IO_VREF sites
can be used as IOs.
The R indicates that these pins are always an IO_VREF regardless of
the device size. The r indicates that these pins are an IO_VREF for some
devices, but not all and in the smaller devices these are just IO.
If designers want to migrate a design from a smaller device to a larger
device in the same package, AND they are using an IO_STANDARD
that requires a VREF source then all R and r pins should be connected
to the same voltage source in the larger device. They should use a
PROHIBIT constraint to prevent an IO from occupying the IO_VREF
sites when doing the design in the smaller device.
End of Record #6110 - Last Modified: 04/06/99 15:58 |
