Solution
For CLIPs to run on a external clock, a dedicated line for the clock has to be configured. For instance we are using a simple adder which is clocked using the "clk" signal.
1. As shown below configure the "
clk" signal as a
clock line in the signal type.

2. Refer to the link
CLIP Tutorial, Part 3: Adding CLIP to a Project , as mentioned in the
step 9, configure the external clock line in the
Clock selection page .