Texas Instruments TMS320DM643x manual Changing PLL Multiplier

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PLL1 Control

5.2.2.2Changing PLL Multiplier

If the PLL is not powered down (PLLPWRDN bit in PLLCTL is cleared to 0) and the PLL stabilization time is previously met (step 7 in Section 5.2.2.1), follow this procedure to change PLL1 multiplier. The recommendation is to stop all peripheral operation before changing the PLL multiplier, with the exception of the C64x+ DSP and DDR2. The C64x+ DSP must be operational to program the PLL controller. DDR2 operates off of the clock from PLLC2.

1.Before changing the PLL frequency, switch to PLL bypass mode:

a.Clear the PLLENSRC bit in PLLCTL to 0 to allow PLLCTL.PLLEN to take effect.

b.Clear the PLLEN bit in PLLCTL to 0 (select PLL bypass mode).

c.Wait for 4 MXI cycles to ensure PLLC switches to bypass mode properly.

2.Clear the PLLRST bit in PLLCTL to 0 (reset PLL).

3.Clear the PLLDIS bit in PLLCTL to 0 (enable the PLL) to allow PLL outputs to start toggling. Note that the PLLC is still at PLL bypass mode; therefore, the toggling PLL output does not get propagated to the rest of the device.

4.Program the required multiplier value in PLLM.

5.If necessary, program PLLDIV1, PLLDIV2, and PLLDIV3 registers to change the SYSCLK1, SYSCLK2, and SYSCLK3 divide values:

a.Check for the GOSTAT bit in PLLSTAT to clear to 0 to indicate that no GO operation is currently in progress.

b.Program the RATIO field in PLLDIV1, PLLDIV2, and PLLDIV3 with the desired divide factors. Note that the dividers must maintain a 1:3:6 ratio to satisfy the CLKDIV1, CLKDIV3, CLKDIV6 clock domain requirements. See the device-specific data manual for more details on Clock Domains. In addition, make sure in this step you leave the PLLDIV1.D1EN, PLLDIV2.D2EN, and PLLDIV3.D3EN bits set (default).

c.Set the GOSET bit in PLLCMD to 1 to initiate a new divider transition. During this transition, SYSCLK1, SYSCLK2, and SYSCLK3 are paused momentarily.

d.Wait for N number of PLLDIVn source clock cycles to ensure divider changes have completed. See Section 5.2.2.3 for the formula on calculating the number of cycles N.

e.Wait for the GOSTAT bit in PLLSTAT to clear to 0.

6.Wait for PLL to reset properly. See the device-specific data manual for PLL reset time.

7.Set the PLLRST bit in PLLCTL to 1 to bring the PLL out of reset.

8.Wait for PLL to lock. See the device-specific data manual for PLL lock time.

9.Set the PLLEN bit in PLLCTL to 1 to remove the PLL from bypass mode.

SPRU978E–March 2008 PLL Controller 41

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