AR# 7937: Foundation 2.1i + SP2: How to instantiate LVDS I/O in Foundation Schematics
AR# 7937
Foundation 2.1i + SP2: How to instantiate LVDS I/O in Foundation Schematics
説明
Keywords: Foundation, fndtn, LVDS,Virtex-E
Urgency: Standard
General Description: With SP2 support for Virtex-E has been added to Foundation 2.1i. However the schematic libraries do not contain LVDS I/O buffer symbols. How can LVDS pins be instantiated in schematics?
ソリューション
Instead of using LVDS buffers use regular IBUFS and OBUFS. Note that for LVDS inputs only one signal is needed whereas for LVDS outputs both, the positive and the negative output (with an inverter) must be drawn.
In the ucf set the IOSTANDARD=LVDS attribute for all IBUFS and OBUFS that should be LVDS.
You can see the reference name in the schematic editor by double clicking on the buffer symbol.
For example, a valid line for an input buffer would be:
INST $I234 IOSTANDARD = LVDS;
Also, for all LVDS I/O the pin locations must be fixed. The implementation tools can not automatically select an I/O pair.
A LVDS input must be LOCed to a positive LVDS pin. The negative pin is selected by the tools. For LVDS outputs both, the positive and the negative pins must be LOCed.
NET INPUT_LVDS LOC = A5; # LVDS INPUT, POSITIVE PIN LOCATION NET OUTPUT_LVDS_POSITIVE LOC = D8; # LVDS POSITIVE OUTPUT PIN LOCATION NET OUTPUT_LVDS_NEGATIVE LOC = C8; # LVDS NEGATIVE OUTPUT PIN LOCATION
Refer to the Virtex-E pinout tables to find the LVDS pin pairs.