PLLDIV1 (/1)
1
0
PLL
0
1
CLKMODE
CLKIN
OSCIN
PLLEN
SYSCLK1
(DDR PHY)
SYSCLKBP
(CLKOUT3)
BPDIV (/8)
PLLM
(programmable)
Pre-DIV
(programmable)
Post-DIV
(/1)
6.4
PLLC Functional Description
6.4.1 Multipliers and Dividers
6.4.2 Bypass Mode
6.4.3 PLL Mode
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PLLC Functional Description
Figure 6-2. PLLC2 Configuration
This section describes the multiplier and dividers in the PLL controller as well as the bypass and PLL
modes of operation.
The PLL controller is capable of programming the PLL controller through the PLL multiplier control register
(PLLM), PLL pre-divider control register (PREDIV), PLL post-divider control register (POSTDIV), and the
PLL system clock divider control registers (PLLDIVn). The dividers are either fixed or programmable. Any
divider may be enabled or disabled. When a divider is disabled, no clock is output from that clock divider,
so a divider only outputs a clock when it is enabled in its corresponding divider control register.
The multiplier PLLM, pre-divider PREDIV, post-divider POSTDIV, and the PLL may be bypassed
altogether. The PLL enable bit (PLLEN) in the PLL control/status register (PLLCTL) determines the PLL
controller mode. When PLLEN = 1, PLL mode is enabled and PLLM, PREDIV, POSTDIV, and the PLL are
used; when PLLEN = 0, bypass mode is enabled and PLLM, PREDIV, POSTDIV, and the PLL are
bypassed. When bypass mode is enabled, the input reference clock is directly input to the system clock
dividers (PLLDIVn). The PLL controller defaults, after reset, to bypass mode.
When in PLL mode (PLLEN = 1), the input reference clock is supplied to divider PREDIV. Divider PREDIV
must be enabled (PREDEN = 1) in PLL mode. When divider PREDIV is enabled, the input reference clock
is divided down by the value in the PLL divider ratio bits (RATIO) in PREDIV. The output from divider
PREDIV is input to the PLL. The PLL multiplies the clock by the value in the PLL multiplier bits (PLLM) in
the PLL multiplier control register (PLLM). The output from the PLL (PLLOUT) is input to the divider
POSTDIV. Divider POSTDIV must be enabled (POSTEN = 1) in PLL mode. When divider POSTDIV is
enabled, the output from the PLL (PLLOUT) is divided down by the value in the PLL divider ratio bits
(RATIO) in POSTDIV. The output from divider POSTDIV is input to the system clock dividers (PLLDIVn).
When enabled (bit DnEN = 1), a system clock divider (PLLDIVn) divides-down the output clock of the PLL
by the value in the PLL divider ratio bits (RATIO) in PLLDIVn. The system clock dividers generate 50%
duty cycle output clocks SYSCLKn.
SPRUFX7 – July 2008
PLL Controllers (PLLCs)
41