Each pin contains local double-data rate (DDR) flip-flop registers in the IOL
for both data and tristate lines. IDDRE1 should be used for instantiating DDR
flip-flops in the input path while ODDRE1 should be used for output and tristate
paths.
Note: Both data and tristate registers must be used in the same manner
(that is both SDR, DDR, or not registered at all).