The AM335x device has two clock inputs. Each clock input passes through an internal oscillator which can be connected to an external crystal circuit (oscillator mode) or external LVCMOS square-wave digital clock source (bypass mode). The oscillators automatically operate in bypass mode when their input is connected to an external LVCMOS square-wave digital clock source. The oscillator associated with a specific clock input must be enabled when the clock input is being used in either oscillator mode or bypass mode.
The OSC1 oscillator provides a 32.768-kHz reference clock to the real-time clock (RTC) and is connected to the RTC_XTALIN and RTC_XTALOUT terminals. This clock source is referred to as the 32K oscillator (CLK_32K_RTC) in the AM335x and AMIC110 Sitara Processors Technical Reference Manual. OSC1 is disabled by default after power is applied. This clock input is optional and may not be required if the RTC is configured to receive a clock from the internal 32k RC oscillator (CLK_RC32K) or peripheral PLL (CLK_32KHZ) which receives a reference clock from the OSC0 input.
The OSC0 oscillator provides a 19.2-MHz, 24-MHz, 25-MHz, or 26-MHz reference clock which is used to clock all non-RTC functions and is connected to the XTALIN and XTALOUT terminals. This clock source is referred to as the master oscillator (CLK_M_OSC) in the AM335x and AMIC110 Sitara Processors Technical Reference Manual. OSC0 is enabled by default after power is applied.
For more information related to recommended circuit topologies and crystal oscillator circuit requirements for these clock inputs, see Section 6.2.2.