The SLICE is the basic logic unit of LatticeECP3 devices, each SLICE
contains two LUT4s. A/B/C/D are input ports of LUT, FCI is input port of
carry chain, F is output port of LUT4, OFX is output port of LUT6, and
FCO is output port of carry chain.
LUT4 delay means A to D inputs to F output, while LUT6 delay means A to D inputs to OFX output.
LUT4 delay is no more than 147ps, 163ps and 179ps for -8, -7 and -6 devices.
LUT6 delay is no more than 273ps, 307ps and 342ps for -8, -7 and -6 devices.
The delay from FCI to FCO is identical to LUT4 delay, while the delay from A/B/C/D to FCO is identical to LUT6 delay.
There are some slightly different delays with different input port of A/B/C/D. In general, D is the fastest, and then C, and then A and B.
For more information, Please access to the weblink below:
http://www.latticesemi.com/documents/ds1021ea.pdf