In this paper the simulation methodology has been useful to establish the effect of a transient interference coupled to a digital communication system. An RFID system according to ISO 14443 type B standard is interfered by transient interference according to EN 61000-4-4 standard producing decision errors. The usage of the software tools employed to analyze the distortion of digital communication systems in convergence of the EM simulation software is a powerful methodology to quantify the degradation of a real digital communication system.