A pattern reading apparatus reads a pattern from a reflective object. Visual stimuli may be presented to a test subject. The antenna comprises dipole radiator that is generally curved to the shape of the meter housing. A latch circuit coupled between the power voltage and the data signal outputs preserves the voltage levels respectively of the complementary pair of data signal outputs when the logic cell operates in the standby mode. The higher class of service guarantees a maximum acceptable restoration time during a path failure.