Problematic Bi-Directional Port Connections: How Well is Your Simulator Filling the UPF LRM Void?

The UPF LRM does not describe in detail the handling of bi-directional (inout) HDL port connections, and this leaves the handling of commonly-used connections open to the interpretation of EDA vendors. In this paper we present two common bi-directional supply port connections that are often the source of unexpected corruption before discussing three possible methods for working around them. We then examine how well each of the three main EDA simulators support the initial scenario and the proposed workarounds. Finally, possible future enhancements to the UPF LRM to ensure well-defined behavior across all tools is discussed.

Brandon Skaggs, Cypress Semiconductor, An Infineon Technologies Company