Smart power meters allow the utility companies to gather more information on power usage than ever before. Instead of someone walking up to a meter to physically read the usage, smart meters can transmit that information in many ways. Radio, Ethernet and Power Line Communication (PLC) are some of the techniques being used. Transistor output optocouplers can be used to isolate the calibration unit from the DSP. These can also be used to isolate the MCU from the clock output. Since data is being output, high-speed optocouplers can be used between the MCU and the communications interface, such as an RS485 protocol.