Texas Instruments OMAP36 Series, Technical Reference Manual

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PRCM
sys_altclk
sys_clkout1
sys_xtalin
sys_xtalout
sys_clkout2
PRM
CM
sys_32k
O
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prcm-035
Device
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PRCM Functional Description
A module can use one or more optional functional clocks. Because an optional functional clock is used
only for specific features of the module, it can be shut down without stopping the module activity (for
example, 54 MHz for the DSS power domain and 96 MHz for the CAM power domain).
3.5.3.2 External Clock I/Os
Figure 3-36 shows the external clock I/Os of the device.
Figure 3-36. External Clock I/O
3.5.3.2.1 External Clock Inputs
3.5.3.2.1.1 32-kHz Always-On Clock
The sys_32k input pin supplies the 32-kHz always-on clock (32K_FCLK clock). This clock is used for
low-frequency operation (timers, debouncing, etc.). It also supplies the WKUP power domain for operation
in the lowest power mode.
3.5.3.2.1.2 High-Frequency System Clock
The high-frequency system clock (SYS_CLK) is supplied to the device from an external clock source
through the sys_xtalin input pin or is generated internally by a local system clock crystal oscillator. In the
latter case, a crystal is connected between the sys_xtalout and sys_xtalin device pins. The sys_boot[6] pin
sets the oscillator operating mode (see
Figure 3-14 ).
The source system clock can be 12, 13, 16.8, 19.2, 26, or 38.4 MHz and can be divided by 2 to provide
the standard system clock frequencies (using internal system clock divider configuration in the
PRCM.
PRM_CLKSRC_CTRL [7:6] SYSCLKDIV bit field). It supplies the reference to the DPLLs and is
also used by several modules. The system clock is activated in the device after the device power-on reset
is released by the reset manager in the PRCM module.
The source-clock selection register (the PRCM. PRM_CLKSEL [2:0] SYS_CLKIN_SEL bit field) is set by
the software to identify the input frequency of the system clock.
Table 3-28 lists the system clock input configurations.
Table 3-28. System Clock Input Configurations
Input Source Device Pin Mapping Description
Quartz sys_xtalin and sys_xtalout Internal oscillator is enabled.
Square clock (1.8-V CMOS signal) sys_xtalin (sys_xtalout is not connected) Internal oscillator is bypassed.
293 SWPU177N – December 2009 – Revised November 2010 Power, Reset, and Clock Management
Copyright © 2009–2010, Texas Instruments Incorporated