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An IOE contains a bidirectional I/O buffer and a register that can be used either as an input register for external data that requires a fast setup time
or as an output register for data that requires fast clock-to-output
performance. In some cases, using an LE register for an input register will
result in a faster setup time than using an IOE register. IOEs can be used
as input, output, or bidirectional pins. The compiler uses the
programmable inversion option to invert signals from the row and
column interconnect automatically where appropriate. For bidirectional
registered I/O implementation, the output register should be in the IOE
and the data input and output enable registers should be LE registers
placed adjacent to the bidirectional pin. Figure 15 shows the bidirectional
I/O registers.
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