TMS570LS3137
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SPNS162.–SEPTEMBER 2011
4.6 Clocks
4.6.1 Clock Sources
The table below lists the available clock sources on the device. Each of the clock sources can be enabled
or disabled using the CSDISx registers in the system module. The clock source number in the table
corresponds to the control bit in the CSDISx register for that clock source.
The table also shows the default state of each clock source.
Table 4-8. Available Clock Sources
Clock
Source #
Name
Description
Default State
0
1
2
3
4
OSCIN
PLL1
Main Oscillator
Output From PLL1
Enabled
Disabled
Disabled
Disabled
Enabled
Reserved
EXTCLKIN1
CLK80K
Reserved
External Clock Input #1
Low Frequency Output of Internal Reference Oscillator
High Frequency Output of Internal Reference
Oscillator
5
CLK10M
Enabled
6
7
PLL2
Output From PLL2
Disabled
Disabled
EXTCLKIN2
External Clock Input #2
4.6.1.1 Main Oscillator
The oscillator is enabled by connecting the appropriate fundamental resonator/crystal and load capacitors
across the external OSCIN and OSCOUT pins as shown in Figure 4-4. The oscillator is a single stage
inverter held in bias by an integrated bias resistor. This resistor is disabled during leakage test
measurement and low power modes.
TI strongly encourages each customer to submit samples of the device to the resonator/crystal
vendors for validation. The vendors are equipped to determine what load capacitors will best tune
their resonator/crystal to the microcontroller device for optimum start-up and operation over
temperature/voltage extremes.
An external oscillator source can be used by connecting a 3.3V clock signal to the OSCIN pin and leaving
the OSCOUT pin unconnected (open) as shown in the figure below.
(see Note B)
OSCIN
Kelvin_GND
OSCOUT
OSCIN
OSCOUT
C1
C2
External
Clock Signal
(toggling 0-3.3V)
(see Note A)
Crystal
(a)
(b)
Note A: The values of C1 and C2 should be provided by the resonator/crystal vendor.
Note B: Kelvin_GND should not be connected to any other GND.
Figure 4-4. Recommended Crystal/Clock Connection
Copyright © 2011, Texas Instruments Incorporated
System Information and Electrical Specifications
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