In the system on a chip, some cells should be placed along a predefined coordinate within a relatively small region. This constraint comes from the requirement that the data should be ready on the common bus at the same time. In this paper, the module placement problem is studied where some modules have the predefined coordinate alignment (PCA) constraint. The relations are given between constrained modules, from which a necessary condition is induced. A polynomial-time algorithm is developed that can guarantee a feasible placement is always obtainable. The algorithm is implemented and tested on ami33 and ami49. The experimental results show that it is effective.