Can I use PWM signal to control devices that requires a system clock - OV7670
many STM32 microcontrollers have a MCO output. (MCO standing for &quot;Master Clock Out&quot;). it's a general purpose clock output which is derived from a flexible selection of various clock sources and a clock prescaler.
here's an image from the STM32F030 datasheet:

The XCLK on 7670 could be from 10MHz to 48MHz. it's not 24MHz necessarily.