The TMC5160 will be operated normally with an external, precisely known clock, as most systems have a microcontroller which has a precise crystal oscillator. An external clock provides well-defined ramp timing and precise motor chopper operation. If an external clock is used, the first rising edge on the clock pin switches to external clock. The TMC5160 adds clock fail-safe circuitry, in case the external clock is lost. When no clock is available, for example in de-centralized drives controlled via the single wire UART interface, the internal clock is often sufficient in order to operate with a precise step rate. Due to factory-trimming, it typically has a tolerance of ±1%. If the internal clock is used, the clock pin must be tied to ground. It must never be left floating, as the first pulse switches off the internal clock generator.