HCLK stands for high-speed clock, the primary timing signal driving the CPU core, memory interfaces, and high-performance buses in a digital system. It dictates the maximum execution speed of the core logic. Engineers route this signal carefully to minimize skew and ensure all fast domains remain synchronized before dividing it down for slower peripherals.
Heard on the job
Check the prescaler settings, because if HCLK is running at 168 megahertz the SPI bus will fail.