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The 5 volt power net on the USB bus is regulated down to 3.3 V using an LDO (low-dropout regulator). An automatic isolation
circuit isolates the LDO when the USB cable is not plugged in.
Power can be injected externally on the VMCU1 net if the USB cable is removed, and no other power sources are present on
the kit. Failure to follow this guideline can cause power conflicts and damage the LDO.
The RM126x can be reset by a few different sources:
▪
A user pressing the RESET button.
▪
The on-board debugger pulling the #RESET pin low.
The kit has one user push button marked BTN0 and one LED marked LED0 that are each connected to a GPIO on the
RM126x. The button is connected to pin PC06 and it is debounced by an RC filter with a time constant of 1 ms. The logic
state of the button is high while the button is not being pressed, and low when the button is pressed. The LED is configurable
in firmware for user’s application. See
BOOT pin (PC06) and BUTTON 0 (silkscreen BTN0)
usage information.
Figure 4: RM126x DVK Button and LED
For the RM126x module the BOOT pin is on PC06 (pin19). On the RM126x development board BTN0 (Button0) is by default
mapped to the BOOT pin for easier utilisation.
The BOOT pin (PC06) is used to determine when execution of the bootloader is required. Upon reset, execution of the
bootloader begins. The state of the BOOT pin is read immediately upon start-up of the bootloader. If LOW (BTN0 pressed),
execution of the bootloader continues, facilitating firmware update via the UART. If the BOOT pin is HIGH (BTN0 not pressed),
the bootloader will stop execution and pass control to the main application firmware.
Please refer to respective DVK schematics and Serial DFU section of User Guide - Firmware Options and Upgrading
–
RM126x Series for more information at:
https://www.lairdconnect.com/rm126x-series
The RM126x Development Kit contains a microcontroller separate from the RM126x that provides the user with an on- board
J-Link debugger through the USB Micro-B port. This microcontroller is referred to as the "on-board debugger
” and is not
programmable by the user. When the USB cable is removed, the on-board debugger goes into a very low power shutoff mode
(EM4S), consuming around 80 nA typically (EFM32GG12 data sheet number).
In addition to providing code download and debug features, the on-board debugger also presents a virtual COM port for
general purpose application serial data transfer. The Packet Trace Interface (PTI) is also supported which offers
invaluable debug information about transmitted and received packets in wireless links.
The figure below shows the connections between the target RM126x device and the on-board debugger. See
more details.
Summary of Contents for RM126 Series
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