The objective of this paper is to suggest the advantages of using SAE J1699 tests and methods as a basis for characterization of physical layer devices. This paper will examine some of the commercially available physical layer IC's that could be used to drive Class B and C multiplex networks. Device characteristics such as propagation delays, current consumption, and common mode will be presented. These characteristics could be used to test device performance in Class B and Class C multiplex applications. Also presented will be an introduction to the new SAE J1699 Recommended Practice for multiplex device testing and how J1699 might be used for physical layer device testing.