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SYSCLK3
DIV4P5 CLK
PLL Controller
0
1
CFGCHIP3[EMA_CLKSRC]
LPSC
EMIFA
Peripheral Clocking
6.3.3 EMIFA Clocking
EMIFA requires a single input clock source. The EMIFA clock can be sourced from either PLL0_SYSCLK3
or DIV4P5 (see
). The EMA_CLKSRC bit in the chip configuration 3 register (CFGCHIP3) of the
System Configuration Module controls whether PLL0_SYSCLK3 or DIV4P5 is selected as the clock
source for EMIFA.
Selecting the appropriate clock source for EMIFA is determined by the desired clock rate.
shows
example PLL register settings and the resulting DIV4P5 and PLL0_SYSCLK3 frequencies based on the
OSCIN reference clock frequency of 25 MHz. From these example configurations, the following
observations can be made:
•
To achieve the maximum frequency (100 MHz) supported by EMIFA and the typical CPU frequency of
300 MHz, the output of the PLL multiplier should be set to 600 MHz and the EMA_CLK source should
be set to PLL0_SYSCLK3 with the PLLDIV3 register set to 3.
•
The frequency of the DIV4P5 clock is fixed at the output frequency of the PLL multiplier block divided
by 4.5.
•
The PLLDIV3 block that sets the divider ratio for PLL0_SYSCLK3 can be changed to achieve various
clock frequencies.
Figure 6-4. EMIFA Clocking Diagram
Table 6-6. EMIFA Frequencies
PLL Multiplier
POSTDIV
PLLDIV3
OSCIN
Register
Multiplier
Post Divider
Output
Register
Frequency
Setting
Frequency
Mode
(1)
Frequency
DIV4P5
Setting
PLL0_SYSCLK3
25
24
600 MHz
Div2
300 MHz
133 MHz
(2)
2
100 MHz
Div3
200 MHz
133 MHz
(2)
2
66.6 MHz
1
100 MHz
Div4
150 MHz
133 MHz
(2)
1
75 MHz
25
18
450 MHz
Div2
225 MHz
100 MHz
3
56.3 MHz
2
75 MHz
Div3
150 MHz
100 MHz
1
75 MHz
Div4
112.5 MHz
100 MHz
1
56.3 MHz
0
112.5 MHz
25
16
400 MHz
Div2
200 MHz
89 MHz
2
66.6 MHz
1
100 MHz
Div3
133 MHz
89 MHz
1
66.5 MHz
Div4
100 MHz
89 MHz
0
100 MHz
(1)
See
for explanation of POSTDIV divider modes.
(2)
The maximum frequency supported by EMIFA is 100 MHz. The 133 MHz is outside of the supported frequency range for EMIFA
and, therefore, is not supported.
66
Device Clocking
SPRUGX5A
–
May 2011
Copyright
©
2011, Texas Instruments Incorporated