In semiconductor manufacturing, finding an efficient way for scheduling a multicluster tool is critical for productivity improvement and cost reduction. This two-part paper analyzes optimal scheduling of multicluster tools equipped with single-blade robots and constant robot moving times. In this first part of the paper, a resource-based method is proposed to analytically derive closed-form expressions for the minimal cycle time of two-cluster tools. We prove that the optimal robot scheduling of two-cluster tools can be solved in polynomial time. We also provide an algorithm to find the optimal schedule. Examples are presented to illustrate the proposed approaches and formulations.