Answers Database
LogiCORE PCI docs: Not clear on how to drive S_READY and S_TERM
Record #5926
Problem Title:
LogiCORE PCI docs: Not clear on how to drive S_READY and S_TERM
Problem Description:
Urgency: Standard
General Description:
In the new PCI documentation (Spartan-XL release):
Page 6-7 states: "The S_READY and S_TERM signals must not be
assigned static values. For timing reasons, these signals should be
driven from the output of a flip-flop, although it is permitted to drive
these signals from combinational logic.
Important: Never tie these signals to logic one or to logic zero."
Then, on page 7-5: "The correct control is achieved by statically
assigning S_READY and S_TERM to values that result in disconnect
with data"
These two statements appear to be contradictory.
Solution 1:
What they're actually trying to say is that the S_READY and S_TERM
signals should not be driven with a VCC or GND. Instead, they should
be driven with a flip-flop whose input is tied to a VCC or GND.
The reason for this is timing-related. If S_READY and S_TERM are
tied with a VCC or GND, then the tools will raname these nets to
some other name, preventing the tools from matching names that
occur in a UCF or guide file.
End of Record #5926 - Last Modified: 03/24/99 11:11 |
