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Hibernate, Current Shunts, Power Supplies, Reset and Crystals (Schematic page 3)

2.3.3 Clocking

The DK-TM4C123G uses a 16.0-MHz crystal (Y2) to complete the TM4C123GH6PGE microcontroller's

main internal clock circuit. An internal PLL, configured in software, multiplies this clock to higher

frequencies for core and peripheral timing.

The Hibernation module is clocked off of an external 32.768 kHz crystal (Y1).

2.3.4 Reset

The RESET signal into the TM4C123GH6PGE microcontroller connects to the RESET switch and to the

ICDI circuit for a debugger-controlled reset.

External reset is asserted (active low) under any one of these conditions:

• Power-on reset

• RESET switch held down

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

supported by all debuggers).

The OLED display has special reset timing requirements requiring a dedicated control line from the

microcontroller.

2.3.5 Power Supplies and Jumper

The DK-TM4C123G can be powered from one of two power sources:

• ICDI USB cable (default)

• USB OTG cable

A moveable jumper shunt on the POWER SELECT headers is used to select one of the two power

sources. Only one source should be selected at a time.

See USB Host/Device/OTG for the recommended jumper positions for the specific USB modes.

The development board is designed to provide power to a limited amount of external circuitry. Table 2-11

shows the board’s power requirements and Table 2-12 shows the board’s breakout limitations.

Table 2-11. Power Requirements

Board Supply Min Typical Max Unit

ICDI USB Cable

4.75 5 5.25 V

USB OTG Cable

Table 2-12. Breakout Requirements

Breakout Condition Max Unit

+3.3V 260 mA

+3.3V at 260mA, OLED on 350 mA

+5.0V

(1) (2)

+3.3V at 260mA, OLED off 380 mA

(1)

This represents the +5.0V breakout and the +V

BUS

breakout. Total current = I

+ I

VBUS

(2)

+5.0V is switched by the load switch (U7); however +V

BUS

is always connected.

SPMU357B–August 2013–Revised March 2014 Hardware Description

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