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Power Management

SPMU365C – March 2014 – Revised October 2016

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Hardware Description

2.2.2 Low Power Modes

The Connected LaunchPad demonstrates several low power microcontroller modes. In run mode, the

microcontroller can be clocked from several sources such as the internal precision oscillator or an external

crystal oscillator. Either of these sources can then optionally drive an internal PLL to increase the effective

frequency of the system up to 120 MHz. In this way, the run mode clock speed can be used to manage

run mode current consumption.

The microcontroller also provides sleep and deep sleep modes and internal voltage adjustments to the

flash and SRAM to further refine power consumption when the processor is not in use but peripherals

must remain active. Each peripheral can be individually clock gated in these modes so that current

consumption by unused peripherals is minimized. A wide variety of conditions from internal and external

sources can trigger a return to run mode.

The lowest power setting of the microcontroller is hibernation, which requires a small amount of supporting

external circuitry available on the Connected LaunchPad. The Connected LaunchPad can achieve

microcontroller current consumption modes under 2 micro-Amps using hibernate VDD3ON mode.

Hibernation with VDD3ON mode is not supported on this board. The Connected LaunchPad can be woken

from hibernate by several triggers including the dedicated wake button, the reset button, an internal RTC

timer and a subset of the device GPIO pins. The hibernation module provides a small area of internal

SRAM that can preserve data through a hibernate cycle.

2.2.3 Clocking

The Connected LaunchPad uses a 25 MHz crystal (Y1) to drive the main TM4C1294NCPDTI internal

clock circuit. Most software examples use the internal PLL to multiply this clock to higher frequencies up to

120 MHz for core and peripheral timing. The 25-MHz crystal is required when using the integrated

Ethernet MAC and PHY.

The Hibernation module is clocked from an external 32.768-KHz crystal (Y3).

2.2.4 Reset

The RESET signal to the TM4C1294NCPDTI microcontroller connects to the RESET switch, BoosterPack

connectors, Breadboard adapter and to the ICDI circuit for a debugger-controller reset.

External reset is asserted (active low) under the following conditions:

•

Power-on reset (filtered by and R-C network)

•

RESET switch is held down.

•

By the ICDI circuit when instructed by the debugger (this capability is optional, and may not be

supported by all debuggers)

•

By an external circuit attached to the BoosterPack or Breadboard connectors.

2.3

Debug Interface

2.3.1 In-Circuit Debug Interface (ICDI)

The Connected LaunchPad comes with an on-board ICDI. The ICDI allows for the programming and

debugging of the TM4C1294NCPDTI using LM Flash Programmer and/or any of the supported tool

chains. Note that ICDI only supports JTAG debugging at this time. It is possible to use other JTAG

emulators instead of the on board ICDI, by connecting to U6. When the ICDI detects an external debug

adapter connection on the JTAG connector U6 and disables the ICDI outputs to allow the external debug

adapter to drive the debug circuit. For more information, see Section 2.3.2.

Debug out of the ICDI is possible by removing resistors R6, R7, R8, R10, R11, R15, R16 and R40 from

the Connected LaunchPad and use the ICDI to drive JTAG signals out on U6 for the purpose of

programming or debugging other boards. To restore the connection to the on-board TM4C1294NCPDTI

microcontroller, install jumpers from the odd to even pins of X1 or re-install the resistors. Removal of R40

disables the detection of an attached external debugger. R40 must be installed to use an external debug

adapter to program or debug the Connected LaunchPad.

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