On the C8051F34A, the ADC can use one of three different voltage reference options: the VDD supply pin, an external reference applied to the VREF pin, or the on-chip 2.4 V reference voltage routed to the VREF pin. In the C8051T620/T320/T321 family, two additional voltage reference options are available. By setting the REGOVR bit in the REF0CN register, the ADC can use the internal regulator as the voltage reference for the ADC. If using the on-chip reference voltage generator, the REFBGS bit can also be used to switch between 1.2 V and 2.4 V. Use of the temperature sensor is very similar to that of the C8051F34A. However, the transfer functions of the temperature sensors on each device family are different. Different values for the offset and slope of the temperature sensor are necessary to accurately calculate the temperature on each device family. Additionally, to help remove some of the error due to part-to-part variations, the temperature sensor output has been measured during production test for each device and stored in EPROM. The value represents the output of the temperature sensor at an ambient temperature of 0°C, if measured with the ADC using the internal regulator as a reference voltage.