Datasheet

2.15. Clocks
2.15.1. Overview
The clocks block provides independent clocks to on-chip and external components. It takes inputs from a variety of
clock sources allowing the user to trade off performance against cost, board area and power consumption. From these
sources it uses multiple clock generators to provide the required clocks. This architecture allows the user flexibility to
start and stop clocks independently and to vary some clock frequencies whilst maintaining others at their optimum
frequencies.
Figure 28. Clocks
overview
For very low cost or low power applications where precise timing is not required, the chip can be run from the internal
Ring Oscillator (ROSC). Alternatively the user can provide external clocks or construct simple relaxation oscillators
using the GPIOs and appropriate external passive components. Where timing is more critical, the Crystal Oscillator
(XOSC) can provide an accurate reference to the 2 on-chip PLLs to provide fast clocking at precise frequencies.
The clock generators select from the clock sources and optionally divide the selected clock before outputting through
enable logic which provides automatic clock disabling in SLEEP mode (see Section 2.11.2).
An on-chip frequency counter facilitates debugging of the clock setup and also allows measurement of the frequencies
of external clocks. The on-chip resus component restarts the system clock from a known good clock if it is accidentally
stopped. This allows the software debugger to access registers and debug the problem.
The chip has an ultra-low power mode called DORMANT (see Section 2.11.3) in which all on-chip clock sources are
stopped to save power. External sources are not stopped and can be used to provide a clock to the on-chip RTC which
can provide an alarm to wake the chip from DORMANT mode. Alternatively the GPIO interrupts can be configured to
wake the chip from DORMANT mode in response to an external event.
Up to 4 generated clocks can be output to GPIOs at up to 50MHz. This allows the user to supply clocks to external
devices, thus reducing component counts in power, space and cost sensitive applications.
RP2040 Datasheet
2.15. Clocks 204