The Clock Generating Circuit built into R8C chips has two oscillator circuits: a main clock oscillator circuit and a On-chip oscillator circuit. The main clock circuit operates at frequencies up to 20MHz, controlled by an external crystal or ceramic resonator. The On-chip oscillator circuit operates without an external resonator and has low-speed (125kHz) and high-speed (8MHz) modes. Speed in the high-speed mode can be adjusted via settings in the High-Speed Ringer Control register 1. This capability can be used to trim any offset back to the nominal frequency, or simply to adjust the clock to a desired rate. For example, the 8MHz nominal high-speed ring output can be adjusted in /-1 ns increments, with a range from 4.319MHz to 16.393MHz. The Clock Generating Circuit provides an Oscillation-Stop Detect function (sometimes called a Clock-Stop Detect function) that can help increase system reliability. For instance, if the external resonator fails or is disconnected from the MCU, the Oscillation Stop Detect function transitions the device from the main clock to the On-chip oscillator so that operation continues or an orderly system shutdown is initiated.