Table 1-40. Low Power Modes
Mode
Description
IDLE
Mode:
This mode is exited by any enabled interrupt. The LPM block itself performs no tasks during this mode.
STANDBY
Mode:
If the LPM bits in the LPMCR0 register are set to 01, the device enters STANDBY mode when the IDLE instruction is
executed. In STANDBY mode the clock input to the CPU (CLKIN) is disabled, which disables all clocks derived from
SYSCLKOUT. The oscillator and PLL and watchdog will still function. Before entering the STANDBY mode, you should
perform the following tasks:
•
Enable the WAKEINT interrupt in the PIE module. This interrupt is connected to both the watchdog and the low
power mode module interrupt.
•
If desired, specify one of the GPIO port A signals to wake the device in the GPIOLPMSEL register. The
GPIOLPMSEL register is part of the GPIO module. In addition to the selected GPIO signal, the XRS input and
the watchdog interrupt, if enabled in the LPMCR0 register, can wake the device from the STANDBY mode.
•
Select the input qualification in the LPMCR0 register for the signal that will wake the device.
When the selected external signal goes low, it must remain low a number of OSCCLK cycles as specified by the
qualification period in the LPMCR0 register. If the signal should be sampled high during this time, the qualification will
restart. At the end of the qualification period, the PLL enables the CLKIN to the CPU and the WAKEINT interrupt is
latched in the PIE block. The CPU then responds to the WAKEINT interrupt if it is enabled.
HALT
Mode:
If the LPM bits in the LPMCR0 register are set to 1x, the device enters the HALT mode when the IDLE instruction is
executed. In HALT mode all of the device clocks, including the PLL and oscillator, are shut down. Before entering the
HALT mode, you should perform the following tasks:
•
Enable the WAKEINT interrupt in the PIE module (PIEIER1.8 = 1). This interrupt is connected to both the watchdog
and the Low-Power-Mode module interrupt.
•
Specify one of the GPIO port A signals to wake the device in the GPIOLPMSEL register. The GPIOLPMSEL register
is part of the GPIO module. In addition to the selected GPIO signal, the XRS input can also wake the device from
the HALT mode.
•
Disable all interrupts with the possible exception of the HALT mode wakeup interrupt. The interrupts can be
re-enabled after the device is brought out of HALT mode.
1.
For device to exit HALT mode properly, the following conditions must be met:
Bit 7 (INT1.8) of PIEIER1 register should be 1.
Bit 0 (INT1) of IER register must be 1.
2.
If the above conditions are met,
a.
WAKE_INT ISR will be executed first, followed by the instructions after IDLE, if INTM = 0.
b.
WAKE_INT ISR will not be executed and instructions after IDLE will be executed, if INTM = 1.
Do not enter HALT low power mode when the device is operating in limp mode (PLLSTS[MCLKSTS] = 1).
If you try to enter HALT mode when the device is already operating in limp mode then the device may not properly enter
HALT. The device may instead enter STANDBY mode or may hang and you may not be able to exit HALT mode. For
this reason, always check that the PLLSTS[MCLKSTS] bit = 0 before entering HALT mode.
When the selected external signal goes low, it is fed asynchronously to the LPM block. The oscillator is turned on and
begins to power up. You must hold the signal low long enough for the oscillator to complete power up. When the signal
is held low for enough time and driven high, this will asynchronously release the PLL and it will begin to lock. Once the
PLL has locked, it feeds the CLKIN to the CPU at which time the CPU responds to the WAKEINT interrupt if enabled.
The low-power modes are controlled by the LPMCR0 register (
System Control and Interrupts
94
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
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