The CASCADE attribute is set to NONE if the delay line is not cascaded. Cascading is used when a delay greater than 1.25 ns is required. The connections between delay elements are shown in This Figure. When using the ODELAYE3 (or IDELAYE3) for cascading, the delay (and the IOB) are no longer available to the design. The delay elements can be cascaded up to the byte boundary in a downward direction. Therefore, the maximum length of the delay depends on where the I/O is placed in the byte.
The routes used to cascade IDELAYE3 and ODELAYE3 are dedicated, high-speed routes. The total fixed intrinsic insertion delay for an IDELAYE3 or ODELAYE3 cascade is the sum of the initial insertion delay plus the cascaded insertion delay. This delay grows as multiple of the times that IDELAYE3 and ODELAYE3 are cascaded. However, the delay is always a fixed value.