There are 64 slice flip-flops in the CLB. Each can be driven by one of multiple sources:
- O5/sum: LUT output in dual LUT mode and SUM output when using carry logic
- O6/cout: LUT output in 6LUT mode and Carry Out output when using carry logic (only on even bits)
- Bypass: each flop has an independent bypass signal
- Miscellaneous: inputs from super long line SLL connections or carry-out of odd bits