Texas Instruments TMS320DM643x manual Core Frequency Flexibility

www.ti.com

Clock Domains

4.2.2 Core Frequency Flexibility

The core frequency domain clocks are supplied by the PLL controller 1 (PLLC1). These domain clocks are flexible, to a degree, within the limitations specified in the device-specific data manual. All of the following frequency ranges and multiplier/divider ratios in the data manual must be adhered to:

∙Input clock frequency range (MXI/CLKIN)

∙PLL1 multiplier (PLLM) range

∙PLL1 output (PLLOUT) frequency range based on the core voltage (1.05V or 1.2V) of the device

∙Maximum device speed

∙PLLC1's SYSCLK3:SYSCLK2:SYSCLK1 frequency ratio must be fixed to 1:3:6. For example, if SYSCLK1 is at 600 MHZ, SYSCLK2 must be at 200 MHZ, and SYSCLK3 must be at 100 MHZ.

As specified in the data manual, the PLLs can be driven by any input ranging from 20 to 30 MHZ. However, a 27 MHZ input is required if the video processing back end (VPBE) subsystem is needed to drive television displays with the integrated video DACs.

Table 4-2shows some example PLL1 multiplier and divider settings assuming MXI/CLKIN frequency of 27 MHZ. The Applicable to Device Core Voltage column indicates whether the setting is allowed for a given device core voltage. For example, the last row in Table 4-2(PLL1 multiplier 22 for a 27 MHZ clock input) only applies to devices with a core voltage 1.2V to meet the PLL1 output (PLLOUT) frequency range required in the data manual. In addition, you must ensure the SYSCLK1 frequency does not exceed the speed grade of the device. For example, for a device rated at 400 MHZ speed grade, SYSCLK1 must not exceed 400 MHZ.

Table 4-2. Example PLL1 Frequencies and Dividers (27 MHZ Clock Input)

		CLKDIV1 Domain		CLKDIV3 Domain		CLKDIV6 Domain		Applicable to Device
		(SYSCLK1)		(SYSCLK2)		(SYSCLK3)		Core Voltage
	PLL1
PLL1	PLLOUT	Divider(1)	Freq	Divider(1)	Freq	Divider(1)	Freq
Multiplier	Freq (MHZ)		(MHZ)		(MHZ)		(MHZ)	1.2V	1.05V
15	405.0	1	405.0	3	135.0	6	67.5	Y	Y
16	432.0	1	432.0	3	144.0	6	72.0	Y	Y
17	459.0	1	459.0	3	153.0	6	76.5	Y	Y
18	486.0	1	486.0	3	162.0	6	81.0	Y	Y
19	513.0	1	513.0	3	171.0	6	85.5	Y	Y
20	540.0	1	540.0	3	180.0	6	90.0	Y	-
21	567.0	1	567.0	3	189.0	6	94.5	Y	-
22	594.0	1	594.0	3	198.0	6	99.0	Y	-
22	594.0	2	297.0	6	99.0	12	49.5	Y	-

(1)The RATIO bit in PLLDIVn is programmed as Divider - 1. For example, for a SYSCLK1 divider of 1, you should program PLLDIV1.RATIO = 0, PLLDIV2.RATIO = 2, PLLDIV3.RATIO = 5.

32	Device Clocking	SPRU978E–March 2008
		Submit Documentation Feedback