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PLL Controllers
7.2.2.2
Initializing PLL Mode from PLL Power Down
If the PLL is powered down (PLLPWRDN bit in PLLCTL is set to 1), perform the following procedure to
initialize the PLL:
1. Program the CLKMODE bit in PLLC0 PLLCTL.
2. Switch the PLL to bypass mode:
(a) Clear the PLLENSRC bit in PLLCTL to 0 (allows PLLEN bit to take effect).
(b) For PLL0 only, select the clock source by programming the EXTCLKSRC bit in PLLCTL.
(c) Clear the PLLEN bit in PLLCTL to 0 (PLL in bypass mode).
(d) Wait for 4 OSCIN cycles to ensure that the PLLC has switched to bypass mode.
3. Clear the PLLRST bit in PLLCTL to 0 (resets PLL).
4. Clear the PLLPWRDN bit in PLLCTL to 0 (brings PLL out of power-down mode).
5. Program the desired multiplier value in PLLM. Program the POSTDIV, as needed.
6. If desired, program PLLDIVn registers to change the SYSCLKn divide values:
(a) Wait for the GOSTAT bit in PLLSTAT to clear to 0 (indicates that no operation is currently in
progress).
(b) Program the RATIO field in PLLDIVn.
(c) Set the GOSET bit in PLLCMD to 1 (initiates a new divider transition).
(d) Wait for the GOSTAT bit in PLLSTAT to clear to 0 (completion of divider change).
7. Set the PLLRST bit in PLLCTL to 1 (brings PLL out of reset).
8. Wait for the PLL to lock. See the device-specific data manual for PLL lock time.
9. Set the PLLEN bit in PLLCTL to 1 (removes PLL from bypass mode).
7.2.2.3
Changing PLL Multiplier
If the PLL is not powered down (PLLPWRDN bit in PLLCTL is cleared to 0), perform the following
procedure to change the PLL multiplier:
1. Switch the PLL to bypass mode:
(a) Clear the PLLENSRC bit in PLLCTL to 0 (allows PLLEN bit to take effect).
(b) For PLL0 only, select the clock source by programming the EXTCLKSRC bit in PLLCTL.
(c) Clear the PLLEN bit in PLLCTL to 0 (PLL in bypass mode).
(d) Wait for 4 OSCIN cycles to ensure that the PLLC has switched to bypass mode.
2. Clear the PLLRST bit in PLLCTL to 0 (resets PLL).
3. Program the desired multiplier value in PLLM. Program the POSTDIV, as needed.
4. If desired, program PLLDIVn registers to change the SYSCLKn divide values:
(a) Wait for the GOSTAT bit in PLLSTAT to clear to 0 (indicates that no operation is currently in
progress).
(b) Program the RATIO field in PLLDIVn.
(c) Set the GOSET bit in PLLCMD to 1 (initiates a new divider transition).
(d) Wait for the GOSTAT bit in PLLSTAT to clear to 0 (completion of divider change).
5. Set the PLLRST bit in PLLCTL to 1 (brings PLL out of reset).
6. Wait for the PLL to lock. See the device-specific data manual for PLL lock time.
7. Set the PLLEN bit in PLLCTL to 1 (removes PLL from bypass mode).
76
Phase-Locked Loop Controller (PLLC)
SPRUGX5A
–
May 2011
Copyright
©
2011, Texas Instruments Incorporated
Содержание AM1802
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