Altera MAX 5000 devices (except the EPM5032, which has only one LAB) and all MAX 7000 devices use a Programmable Interconnect Array ( PIA ), shown in Figure 7.8 . The PIA is a cross-point switch for logic signals traveling between LABs. The advantages of this architecture (which uses a fixed number of connections) over programmable interconnection schemes (which use a variable number of connections) is the fixed routing delay. An additional benefit of the simpler nature of a large regular interconnect structure is the simplification and improved speed of the placement and routing software.
Figure 7.8 (a) illustrates that the delay between any two LABs, t PIA , is fixed. The delay between LAB1 and LAB2 (which are adjacent) is the same as the delay between LAB1 and LAB6 (on opposite corners of the die). It may seem rather strange to slow down all connections to the speed of the longest possible connection—a large penalty to pay to achieve a deterministic architecture. However, it gives Altera the opportunity to highly optimize all of the connections since they are completely fixed.