The TMC2130 can be operated with an external, precisely known clock, as systems commonly have a microcontroller with a precise crystal oscillator. When no clock is available, or when the additional wiring shall be reduced, the internal clock can be used. If the internal clock is used, the CLK pin must be tied to ground. It must never not be left floating, as the first pulse switches off the internal clock generator. If an external clock is used, the first rising edge on the CLK pin switches to external clock. It necessary to ensure that the external CLK is always present during operation, if it is missing, the driver should be disabled using ENN pin to prevent the driver stage from remaining in continuous on conditions.