LM3S1607 Luminary Micro, Inc, LM3S1607 Datasheet - Page 67

• Manufacturer Part Number: LM3S1607
• Description: Lm3s1607 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

6.1.5.6
6.1.6
June 02, 2008
Main Oscillator Verification Circuit
A circuit is added to ensure that the main oscillator is running at the appropriate frequency. The
circuit monitors the main oscillator frequency and signals if the frequency is outside of the allowable
band of attached crystals.
The detection circuit is enabled using the CVAL bit in the Main Oscillator Control (MOSCCTL)
register. If this circuit is enabled and detects an error, the following sequence is performed by the
hardware:
1.
2.
3.
4.
5.
System Control
For power-savings purposes, the RCGCn , SCGCn , and DCGCn registers control the clock gating
logic for each peripheral or block in the system while the controller is in Run, Sleep, and Deep-Sleep
mode, respectively.
In Run mode, the processor executes code. In Sleep mode, the clock frequency of the active
peripherals is unchanged, but the processor is not clocked and therefore no longer executes code.
In Deep-Sleep mode, the clock frequency of the active peripherals may change (depending on the
Run mode clock configuration) in addition to the processor clock being stopped. An interrupt returns
the device to Run mode from one of the sleep modes; the sleep modes are entered on request from
the code. Each mode is described in more detail below.
There are four levels of operation for the device defined as:
■
■
■
Run Mode. Run mode provides normal operation of the processor and all of the peripherals that
are currently enabled by the RCGCn registers. The system clock can be any of the available
clock sources including the PLL.
Sleep Mode. Sleep mode is entered by the Cortex-M3 core executing a WFI (Wait for
Interrupt) instruction. Any properly configured interrupt event in the system will bring the
processor back into Run mode. See the system control NVIC section of the ARM® Cortex™-M3
Technical Reference Manual for more details.
In Sleep mode, the Cortex-M3 processor core and the memory subsystem are not clocked.
Peripherals are clocked that are enabled in the SCGCn register when auto-clock gating is enabled
(see the RCC register) or the RCGCn register when the auto-clock gating is disabled. The system
clock has the same source and frequency as that during Run mode.
Deep-Sleep Mode. Deep-Sleep mode is entered by first writing the Deep Sleep Enable bit in
the ARM Cortex-M3 NVIC system control register and then executing a WFI instruction. Any
properly configured interrupt event in the system will bring the processor back into Run mode.
See the system control NVIC section of the ARM® Cortex™-M3 Technical Reference Manual
for more details.
The Cortex-M3 processor core and the memory subsystem are not clocked. Peripherals are
clocked that are enabled in the DCGCn register when auto-clock gating is enabled (see the RCC
The MOSCFAIL bit in the Reset Cause (RESC) register is set.
If the internal oscillator (IOSC) is disabled, it is enabled.
The system clock is switched from the main oscillator to the IOSC.
A system-wide reset is initiated that lasts for 32 IOSC periods.
Reset is de-asserted and the processor is directed to the NMI handler during the reset sequence.
Preliminary
LM3S1607 Microcontroller
67