IOB (input - output blocks)

These provide connection between the internal logic and external package pins. XC4000 devices have between 64 and 192 IOBs, Figure 187. Each IOB is configurable and consists of

1 external pin, which can serve as
- input,
- output, or
- bidirectional
registers
3-state mode
testing facilities, etc

**Figure 187:** Input-output block.
$\begin{figure} \begin{center} \epsfig{file=images/iob.eps}\end{center}\end{figure}$

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