Zastosowanie diagramów BDD w syntezie logicznej dla układów typu PAL

W artykule przedstawiono zastosowanie diagramów BDD w procesie syntezy dla układów typu PAL. Diagramy BDD wykorzystywane są w procesie dekompozycji funkcji w celu szybkiego wyszukania możliwych do implementacji w pojedynczej komórce PAL podukładów.

The paper presents the BDD based method of function decomposition for PAL-based devices. A BDD diagram is successfully used for function mapping for LUT based FPGAs [3]. In opposite to LUT-based circuits PAL-based devices are limited in number of products while number of inputs to the block is large (Fig. 1). Before decomposition procedure can be applied, function variables are ordered. Decomposition procedure searches BDD tree for suitable decomposition starting from variables with the largest index (just above terminals 0 and 1). When satisfying function is found its subtree is substituted by node that belong to newly created variable (Fig. 3 a,b,c,d). Procedure is applied iteratively until root node is reached. Decomposition procedure efficiency is proofed with use of ISCAS LG89 benchmarks. Obtained implementation results are compared to classical approach in Tab. 1.