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Question: How do you configure the I/O standards for the ports in full flex devices?
Answer: There are two port standard pins available for each of the ports, left and right, which can be configured to select the I/O standard of the port. The HIGH/LOW conditions of the PORTSTD[0:1] pins will determine the standard for the I/O pins of that particular port. Table 1 gives the list of standards available for the I/Os and the corresponding states for the PORTSTD[0:1] pins.
Table 1. I/O Standards and Their Corresponding States
| PORTSTD1 | PORTSTD0 | I/O Standard |
| VSS | VSS | LVTTL |
| VSS | VTTL | HSTL |
| VTTL | VSS | 2.5V LVCMOS |
| VTTL | VTTL | 1.8 LVCMOS |
The PORTSTD[0:1] pins will be operated on LVTTL. Here VTTL stands for the 3.3 V LVTTL supply itself. For example, if you need the 1.8 LVCMOS standard for your I/O pins, then you need to connect PORTSTD[0:1] pins to the 3.3 V supply.
