Spartan-6 FPGA SelectIO Resources User Guide 笔记2 SelectIO Attributes/Constraints

1.Location Constraint   用于分配I/O端口

NET <I/O_NAME> LOC = "<EXTERNAL_PORT_IDENTIFIER>";

Example:

NET MY_IO LOC=R7;

2.IOSTANDARD Attribute 用于选择IO标准如LVCMOS25，LVDS_25等

NET <I/O_NAME> IOSTANDARD=”<IOSTANDARD VALUE>”;

3.Output Slew Rate Attributec 

NET <I/O_NAME> SLEW = "<SLEW_VALUE>";

SLEW_VALUE can SLOW (Default)   FAST  QUIETIO

4.Output Drive Strength Attribute 驱动能力（mA）

NET <I/O_NAME> DRIVE = "<DRIVE_VALUE>"; 

DRIVE_VALUE can 2 4 6 8 12 (Default) 16 24

5.PULLUP/PULLDOWN/KEEPER for IBUF, OBUFT, and IOBUF 
NET <I/O_NAME> <PULLUP/PULLDOWN/KEEPER>;