FRDM-K28F hardware description
Freedom Board for Kinetis K28F (FRDM-K28F), User's Guide, Rev. 0, 04/2017
8
NXP Semiconductors
programming interface, virtual serial port interface, and CMSIS-DAP debug protocol interface. For
more information about the OpenSDA v2.2 software, see
mbed.org
and
github.com/mbedmicro/CMSIS-
DAP
.
OpenSDAv2
OpenSDA MCU
K20DX128Vxx5
MSD Bootloader
OpenSDAv2
Application
UART TX/RX
GPIO
Serial Terminal
File System
SWD/JTAG
LED
PWM
USB Host
IDE
GPIO/ADC
SPI, GPIO
USB
Target
Processor
nRESET
UART RX/TX
Figure 4. OpenSDA high-level block diagram
OpenSDA v2.2 is managed by the Kinetis K20 MCU built upon the ARM Cortex-M4 core.
The OpenSDA v2.2 circuit includes a status LED (D3) and a push-button (SW1). The push-button
asserts the reset signal to the K28F target MCU. It can be also used to place the OpenSDA v2.2 circuit
into the bootloader mode. The SPI and GPIO signals provide an interface to either the SWD debug port
or the K20. Additionally, signal connections are available to implement the UART serial channel. The
OpenSDA v2.2 circuit receives power when the USB connector J6 is plugged into a USB host.
3.2.1. Debug interface
Signals with the UART and GPIO capability are used to connect directly to the SWD of the K28F.
These signals are also brought out to the standard 10-pin (0.05”) Cortex debug connector (J23). It is
possible to isolate the K28F MCU from the OpenSDA v2.2 circuit and use J23 to connect to an
off-board MCU. To do this, cut the trace on the bottom side of the PCB that connects the J17 pin 2 to the
J23 pin 4. This disconnects the SWD_CLK pin from the K28F so that it does not interfere with the
communication to an off-board MCU connected to J17.
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