A programmable I/O element for an I/O terminal of a logic array is suitable
for operating according to high speed 110 modes such as double data rate
and zero bus turnaround. The I/O element may include an input block with
two registers for registering input signals from the terminal upon
alternate clock edges. In addition or alternatively, it may include an
output block with two registers that separately register output signals
from the array on the same clock edge and a multiplexer that alternately
outputs those signals. For bidirectional terminals, the multiplexer output
is connectable to the I/O terminal via an output buffer, and an output
enable block provides an enable signal to a gating input of the output
buffer. Programmable delays may be included in the input, output, and
output enable paths, in particular to provide a slower turn-on time than
turn-off time for the output buffer.
