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PLL Controllers
7.2.2 Steps for Programming the PLLs
Note that there is a lock mechanism implemented to protect the PLL controller registers. See
for information on unlocking the PLL controller registers.
Refer to the appropriate subsection on how to program the PLL clocks:
•
If the PLL is powered down (PLLPWRDN bit in PLLCTL is set to 1), follow the full PLL initialization
procedure in
.
•
If the PLL is not powered down (PLLPWRDN bit in PLLCTL is cleared to 0), follow the sequence in
to change the PLL multiplier.
•
If the PLL is already running at a desired multiplier and only the SYSCLK dividers will be updated,
follow the sequence in
Note that the PLLs are powered down after a Power-on Reset (POR). The PLLs are not powered down
after a Warm Reset (RESET), but the PLLEN bit in PLLCTL is cleared to 0 (bypass mode) and the
PLLDIVx registers are reset to default values.
7.2.2.1
Locking/Unlocking PLL Register Access
A lock mechanism is implemented on the device to prevent inadvertent writes to the PLL controller
registers. This provides protection from stopping modules when the module clocks are disabled. For
example, the watchdog timer that runs on the PLL0_AUXCLK will stop if this PLL clock is unintentionally
disabled.
The PLL lock bits are located within the system configuration (SYSCFG) module:
•
When set, the PLL_MASTER_LOCK bit in the chip configuration 0 register (CFGCHIP0) locks PLLC0.
•
When set, the PLL1_MASTER_LOCK bit in the chip configuration 3 register (CFGCHIP3) locks PLLC1.
Because the SYSCFG module has its own lock mechanism, the SYSCFG module must be unlocked first
by writing to the KICK0R and KICK1R registers before the PLL lock bits can be cleared. Like the KICK
registers, the PLL lock bits can only be modified while in a privileged mode. See
for
information on privilege type and the KICK0R and KICK1R registers.
NOTE:
The PLL_MASTER_LOCK bit in CFGCHIP0 and the PLL1_MASTER_LOCK bit in
CFGCHIP3 default to unlocked after reset, so the following procedure is only required if the
PLLs have been locked (set to 1).
To modify the PLL controller registers, use the following sequence:
1. Write the correct key values to KICK0R and KICK1R registers.
2. Clear the PLL_MASTER_LOCK bit in CFGCHIP0 and/or the PLL1_MASTER_LOCK bit in CFGCHIP3,
as required.
3. Configure the desired PLL controller register values.
4. Set the PLL_MASTER_LOCK bit in CFGCHIP0 and/or the PLL1_MASTER_LOCK bit in CFGCHIP3,
as required.
5. Write an incorrect key value to the KICK0R and KICK1R registers.
75
SPRUGX5A
–
May 2011
Phase-Locked Loop Controller (PLLC)
Copyright
©
2011, Texas Instruments Incorporated
Содержание AM1802
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