1.3.2.8 XCLKOUT Generation
The XCLKOUT signal is directly derived from the system clock SYSCLKOUT as shown in
XCLKOUT can be either equal to, one-half, or one-fourth of SYSCLKOUT. By default, at power-up, XCLKOUT =
SYSCLKOUT/4 or XCLKOUT = OSCCLK/16.
CLKIN
28x CPU
SYSCLKOUT
0,0
0,1
1,0
XCLKOUT
Pin
XCLK[XCLKOUTDIV]
PLL
PLL Bypass
OSCCLK
Default at reset
PLLCR
0
n
n
≠
0
0
or
1
3
/2
PLLSTS[DIVSEL]
2
/4
/4
/2
Figure 1-42. XCLKOUT Generation
If XCLKOUT is not being used, it can be turned off by setting the XCLKOUTDIV bit to 3 in the XCLK register.
1.3.2.9 External Reference Oscillator Clock Option
TI recommends that customers have the resonator/crystal vendor characterize the operation of their device
with the DSP chip. The resonator/crystal vendor has the equipment and expertise to tune the tank circuit. The
vendor can also advise the customer regarding the proper tank component values to provide proper start-up and
stability over the entire operating range.
1.3.3 Low-Power Modes Block
summarizes the various modes.
The various low-power modes operate as shown in
Refer to the device data sheet for exact timing for entering and exiting the low power modes.
Table 1-39. Low-Power Mode Summary
Mode
LPMCR0[1:0]
OSCCLK
CLKIN
SYSCLKOUT Exit
IDLE
00
On
On
On
XRS,
Watchdog interrupt,
Any enabled interrupt
STANDBY
01
On
(watchdog still running)
Off
Off
XRS,
Watchdog interrupt,
GPIO Port A signal,
Debugger
HALT
1X
Off
(oscillator and PLL turned off,
watchdog not functional)
Off
Off
XRS,
GPIO Port A Signal,
Debugger
(1)
The Exit column lists which signals or under what conditions the low power mode is exited. This signal must be kept low long enough
for an interrupt to be recognized by the device. Otherwise the IDLE mode is not exited and the device goes back into the indicated low
power mode.
(2)
On the 28x, the JTAG port can still function even if the clock to the CPU (CLKIN) is turned off.
System Control and Interrupts
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
93
Copyright © 2022 Texas Instruments Incorporated
Summary of Contents for TMS320 2806 Series
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