NXP Semiconductors FRDM-K28F User manual

© 2017 NXP B.V.
Freedom Board for Kinetis K28F
(FRDM-K28F)
1.Introduction
The Freedom development platform is a set of software
and hardware tools for evaluation and development. It
is ideal for rapid prototyping of MCU-based
applications. The Freedom K28 board (FRDM-K28F)
is a simple yet sophisticated design featuring the
Kinetis K series MCU built upon the ARM®
Cortex®-M4 core which features a Floating-Point Unit
(FPU).
FRDM-K28F can be used to evaluate the K27 and K28
Kinetis K series MCUs. The FRDM-K28F board
features the MK28FN2M0VMI15 MCU which features
a maximum operating frequency of 150 MHz, 2 MB
flash, 1 MB RAM, high-speed and full-speed USB
controller with available crystal-less operation,
SDRAM controller, secure digital host controller,
QuadSPI controller, and analog and digital peripherals.
The FRDM-K28F hardware is form-factor compatible
with the Arduino™R3 pin layout, providing a broad
range of expansion board options. The on-board
interface includes a 6-axis digital accelerometer and
magnetometer, RGB LED, FlexIO socket, SD card
interface, mobile SDRAM memory, and external serial
flash memory.
NXP Semiconductors
Document Number: FRDMK28FUG
User's Guide
Rev. 0
,
04/2017
Contents
1. Introduction........................................................................1
2. FRDM-K28F hardware overview ......................................2
3. FRDM-K28F hardware description....................................4
3.1. Power supply...........................................................4
3.2. Serial and Debug Adapter version 2 (OpenSDA
v2.2) ................................................................................7
4. MCU ..................................................................................9
5. Clocking...........................................................................10
6. Universal Serial Bus (USB) .............................................11
7. VBAT...............................................................................12
8. Accelerometer and magnetometer....................................13
9. RGB LED.........................................................................14
10. Serial port.........................................................................15
11. QuadSPI memory.............................................................15
12. Mobile SDRAM memory.................................................15
13. Secure Digital (SD) card..................................................15
14. FlexIO socket...................................................................16
15. Reset.................................................................................17
16. Push-button switches........................................................17
17. Visible light sensor...........................................................18
18. Debug...............................................................................19
19. Input/output connectors....................................................19
20. Arduino compatibility......................................................20
21. Jumper table.....................................................................20
22. References........................................................................21
23. Revision history ...............................................................21
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FRDM-K28F hardware overview
Freedom Board for Kinetis K28F (FRDM-K28F), User's Guide, Rev. 0, 04/2017
2 NXP Semiconductors
FRDM-K28F features OpenSDA v2.2, the open-source hardware embedded serial and debug adapter
running an open-source bootloader. This circuit offers several options for serial communication, flash
programming, and run-control debugging. OpenSDA v2.2 is an mbed™HDK-compatible debug
interface pre-loaded with the open-source DAP link interface firmware for rapid prototyping and
product development with focus on the connected Internet of Things (IoT) devices.
2.FRDM-K28F hardware overview
The features of the FRDM-K28F board are:
•Kinetis MK28FN2M0VMI15 MCU (ARM Cortex-M4 at150 MHz, 1 MB SRAM, 2 MB flash,
HS and FS USB, 169 MAPBGA package).
•Kinetis K20 MCU (K20DX128VFM5) based OpenSDA circuit.
•Dual-role high-speed and full-speed USB interface with the micro-B USB connector via the
high-speed switch.
•One 256 Mbit (32 MB) on-board QuadSPI memory at 1.8 V.
•One 128 Mbit (16 MB) on-board mobile SDRAM memory at 3.3 V.
•Multiple independent voltage domains: VDD_CORE, VDD, VBAT, and VDDIO_E.
•FlexIO socket which enables you to connect an optional TFT Proto 5” CAPACITIVE from
MikroElektronika (5” display board with capacitive touch).
•Easy access to the MCU input/output through Arduino R3-compatible I/O connectors to connect
external add-on boards.
•Flexible power supply option—OpenSDA v2.2 USB, Kinetis K28 USB, or an external source.
•FXOS8700CQ—6-axis sensor with accelerometer and magnetometer.
•RGB LED.
•Two mechanical push-buttons for user input and one for the reset.
•Programmable OpenSDA v2.2 debug circuit supporting the DAP-Link interface software which
provides:
—Mass-Storage Device (MSD) flash programming interface.
—CMSIS-DAP debug interface over a driverless USB HID connection providing
run-control debugging and compatibility with the IDE tools.
—Virtual serial port interface.
—Open-source CMSIS-DAP software project.
Figure 1 shows the block diagram of the FRDM-K28F board. The primary components and their
placement on the hardware assembly are shown in Figure 2.
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FRDM-K28F hardware overview
Freedom Board for Kinetis K28F (FRDM-K28F), User's Guide, Rev. 0, 04/2017
NXP Semiconductors 3
Figure 1. FRDM-K28F block diagram
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FRDM-K28F hardware description
Freedom Board for Kinetis K28F (FRDM-K28F), User's Guide, Rev. 0, 04/2017
4 NXP Semiconductors
Figure 2. FRDM-K28F primary component placement
3.FRDM-K28F hardware description
3.1. Power supply
There are multiple power supply options on the FRDM-K28F board. It can be powered from either of
the USB connectors, the VIN pin on the I/O header, or an off-board 1.71 V–3.6 V supply from the 3.3 V
pin on the I/O header. The USB and VIN supplies are regulated on-board using a 3.3 V linear regulator
to produce the main power supply and a 1.8 V linear regulator to produce the VDDIO_E power supply.
A direct voltage supply to the K28F MCU is also available via J18, J15, and J22. The following table
provides the operational details and requirements for the power supplies.
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FRDM-K28F hardware description
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Table 1. FRDM-K28F power requirements
Supply source
Valid range
OpenSDA v2.2 operational
Regulated on-board
OpenSDA v2.2 USB
5 V
Yes
Yes
K28F USB
5 V
No
Yes
P5-9V_VIN pin
5 V–9 V
No
Yes
3.3 V VDD header (J18)
1.71 V–3.6 V
No
No
1.8 V VDDIO_E header (J15)
1.71 V–3.6 V
No
No
1.2 V VDD_CORE header (J22)
1.17 V–1.32 V (RUN mode)
1.33 V–1.47 V (HSRUN mode)
No
No
NOTE
The OpenSDA v2.2 circuit is only operational when a USB cable is
connected and supplies power to the OpenSDA v2.2 USB. However, a
protection circuitry is provided to enable multiple sources to be powered
at once. By default, the FRDM-K28F VDD_CORE = 1.2 V is operating in
the RUN mode. To operate in the HSRUN mode, supply 1.33 V–1.47 V
externally.
CAUTION
When 3.3 V is supplied directly through the Freedom platform
compatibility header J3, enable the protection diode D9 by opening the
J26 shorting header.
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FRDM-K28F hardware description
Freedom Board for Kinetis K28F (FRDM-K28F), User's Guide, Rev. 0, 04/2017
6 NXP Semiconductors
Figure 3. Power supply schematic
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FRDM-K28F hardware description
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Table 2. FRDM-K28F power supplies
Power supply
name
Description
Notes
P5-9V_VIN
Power supply from the VIN pin of the I/O
headers (J3 pin 16). Sources the main 3.3 V
voltage regulator and the optional 5 V regulator
at J25. A Schottky diode provides the
back-drive protection.
—
P3V3_VREG
Regulated 3.3 V supply. Sources power to the
P3V3 supply rail. A back-drive protection
Schottky diode (D9) is provided to enable an
external 2.7 V–3.3 V supply connection at the
J3 header P3V3 pins.
Open J26 (shorted on the bottom of the board)
if the J3 header P3V3 pins are used to supply
an alternate voltage from the on-board 3.3 V
supply.
VDD_K28F
K28F MCU voltage supply. Select the 3.3 V or
1.8 V regulator options at header J20, or the
2.7 V–3.3 V P3V3 inputs on the J3 header.
Header J18 provides a convenient means for
energy consumption measurements.
The IS42SM16800H-6BLI SDRAM is a 3.3 V
component. Open J10 (shorted on the bottom
of the board) if the VDD_K28F node is less
than 2.7 V.
VDDIO_E_1V8
K28F VDDIO_E MCU voltage supply. Header
J15 provides a convenient means for energy
consumption measurements.
The MT25QU256ABA1EW7-0SIT QSPI flash
is a 1.8 V component. Open J16 (shorted on
the bottom of the board) if the VDDIO_E_1V8
node is ever raised above 1.8 V.
VDDCORE_1V2
K28F VDD_CORE MCU voltage supply.
Header J22 provides a convenient means for
energy consumption measurements.
—
P3V3
Main supply for the 3 V MCU VDD and
peripheral functions. Supplies nominal 3 V at
the J3 header P3V3 nodes. Sourced from the
P3V3_VREG or P3V3 inputs on the J3 I/O
header.
When the J3 P3V3 inputs are used, the voltage
must be in the 2.7 V–3.3V range. See the
VDD_K28F note.
P1V8
Power supply for the 1.8 V MCU VDDIO_E
pins and the QSPI peripheral. P1V8 can be
selected as the MCU VDD source at header
J20.
See the VDD_K28F note if P1V8 is selected as
the source at header J20.
VDD
Supply the voltage for the MCU and many
board functions. Select the 3.3 V or 1.8 V
regulator options on header J20, or the P3V3
inputs on the J3 header.
When the J3 P3V3 inputs are used, the voltage
must be in the 2.7 V–3.3 V range. See the
VDD_K28F note.
P3V3_SDA
OpenSDA v2.2 circuit 3.3 V supply generated
on the K20DX from the USB cable VBUS
signal.
—
P5V
Nominal 5 V supplied to the I/O headers (J3
pin 10).
—
3.2. Serial and Debug Adapter version 2 (OpenSDA v2.2)
OpenSDA v2.2 is a serial and debug adapter circuit which includes open-source hardware design,
open-source bootloader, and debug interface software. It bridges the serial and debug communications
between the USB host and the embedded target processor, as shown in the following figure. The
hardware circuit is based on the Kinetis K20 family MCU with 128 KB of embedded flash and an
integrated USB controller. OpenSDA v2.2 is pre-loaded with the CMSIS-DAP bootloader (an open-
source MSD bootloader), and the DAP-Link interface firmware which provides the MSD flash
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FRDM-K28F hardware description
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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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MCU
Freedom Board for Kinetis K28F (FRDM-K28F), User's Guide, Rev. 0, 04/2017
NXP Semiconductors 9
Figure 5. SWD debug connector
The J23 header is populated by default. A mating cable (such as the Samtec FFSD IDC cable) can then
be used to connect the OpenSDA v2.2 of the FRDM-K28F to an off-board SWD connector.
3.2.2. Virtual serial port
A serial port connection is available between the OpenSDA v2.2 MCU and pins PTC24 and PTC25 of
the K28 MCU.
4.MCU
FRDM-K28F features the MK28FN2M0VMI15 MCU. This 150 MHz MCU is a part of the Kinetis K2x
family and it is implemented in the 169 MAPBGA and 210 WLCSP (K28 only) packages. The
FRDM-K28F board also supports the K27 and K28 MCUs. The following table describes some of the
features of the MK28FN2M0VMI15 MCU that is populated on this board.
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Clocking
Freedom Board for Kinetis K28F (FRDM-K28F), User's Guide, Rev. 0, 04/2017
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Table 3. MK28FN2M0VMI15 MCU features
Feature
Description
Performance
•Up to 150 MHz ARM Cortex-M4-based core with DSP instructions and a
single precision floating-point unit.
Memory and memory expansion
•2 MB program flash memory and 1 MB RAM.
•Dual QuadSPI with XIP.
•FlexBus external bus interface and SDRAM controller.
Analog modules
•One 16-bit SAR ADC, two 6-bit DACs, and one 12-bit DAC.
•Two analog comparators (CMP) containing a 6-bit DAC and a
programmable reference input.
•Voltage reference: 1.2 V.
Communication interfaces
•USB high-speed device/host.
•USB full-/low-speed on-the-go controller with the device charge detect
capability.
•Secure Digital Host Controller (SDHC).
•FlexIO.
•Two I2S modules, four SPI modules (SPI3 supports more than 40 Mbit/s),
four I2C modules, and five LPUART modules.
Security
•Hardware random-number generator.
•Supports DES, AES, and SHA accelerator (CAU).
•Cyclic Redundancy Check (CRC).
•Multiple levels of embedded flash security.
Timers
•One 4-channel 32-bit periodic interrupt timer.
•Two 16-bit low-power timer PWM modules.
•Two 8-channel motor-control/general-purpose/PWM timers.
•Two 2-channel quadrature decoder/general-purpose timers.
•Real-time clock with an independent 3.3 V power domain.
•Programmable delay block.
Human machine interface
•Up to 120 general-purpose inputs/outputs.
Operating Characteristics
•Main VDD voltage and flash write voltage range: 1.71 V–3.6 V.
•Temperature range (ambient): -40–105°C.
•Independent VDD_CORE: 1.17 V-1.47 V.
•Independent VDDIO for PORTE (QuadSPI): 1.71 V–3.6 V.
•Independent VBAT (RTC): 1.71 V–3.6 V.
5.Clocking
CAUTION
The resonator is not recommended when the HS USB is used.
The K28F MCU starts up from an internal Digitally-Controlled Oscillator (DCO). Software can enable
the main external oscillator (EXTAL0/XTAL0) if desired. The external oscillator/resonator can range
from 32.768 kHz up to 32 MHz. The default external source for the MCG oscillator inputs (EXTAL) is
the 12 MHz crystal, which is configured to operate in the low-power mode, so the feedback resistor
(R78) is not needed. The 12 MHz reference clock is suitable for both the audio codec and the HS USB
features.
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Universal Serial Bus (USB)
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Figure 6. 12 MHz crystal clock source for MCU
By default, the 32.768 KHz crystal is connected to the K28F MCU’s RTC oscillator inputs.
Figure 7. 32.768 kHz crystal for RTC
6.Universal Serial Bus (USB)
The MK28FN2M0VMI15 MCU features the HS USB with the host/device capability and a
full-speed/low-speed USB module with the on-the-go/host/device capability and a built-in transceiver.
The FRDM-K28F board routes the USB D+ and D signals from the MK28FN2M0VMI15 MCU to the
high-speed analog switch (NXP NX3DV42), selecting between the HS and FS USB signals to the
on-board micro USB connector (J24).
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VBAT
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Figure 8. K28F USB port
When the FRDM-K28F board operates in the USB host mode, J13 must be shunted to supply 5 V to
VBUS (J24 pin 1). The 5 V source can be the OpenSDA v2.2 USB port (J6) or the optional 5 V
regulator populated at J25 and supplied by P5-9V_VIN at pin 16 of the J3 connector.
Figure 9. K28F USB port power inputs for host mode
7.VBAT
The Real-Time Clock (RTC) module is powered on its own domain. FRDM-K28F provides a battery
holder for a coin cell battery that can be used as the VBAT supply. The holder supports common 20 mm
diameter 3 V lithium coin cell batteries (for example, 2032 and 2025).
If a coin cell battery is used, add a small amount of solder to the coin cell ground pad before adding the
battery holder.
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Accelerometer and magnetometer
Freedom Board for Kinetis K28F (FRDM-K28F), User's Guide, Rev. 0, 04/2017
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Figure 10. Coin cell
8.Accelerometer and magnetometer
The FXOS8700CQ low-power, six-axis sensor with the accelerometer and magnetometer is interfaced
through the I2C bus and two GPIO signals, as shown in the following table. By default, the I2C address
is 0x1C (pull-up on SA1 and pull-down on SA0).
Table 4. Accelerometer and magnetometer signal connection
FXOS8700Q
K28F connection
SCL
PTC29/ I2C3_SCL
SDA
PTC28/ I2C3_SDA
INT1
PTC26
RST
PTC27
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RGB LED
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Figure 11. Accelerometer and magnetometer
9.RGB LED
The RGB LED is connected through the GPIO pins. The signal connections are shown in the following
table. Note that the RGB LED operates in the range of the MCU supply voltage.
Table 5. LED signal connection
RGB LED
K28F connection
RED
PTE6
GREEN
PTE7
BLUE
PTE8
Figure 12. Accelerometer and magnetometer
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Secure Digital (SD) card
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NXP Semiconductors 15
10. Serial port
The primary serial port interface signals are PTC24 LPUART0_RX_TGTMCU and PTC25
LPUART0_TX_TGTMCU. These signals are connected to the OpenSDA v2.2 circuit.
11. QuadSPI memory
FRDM-K28F includes a single QuadSPI memory with Execute in Place (XiP). The on-board QuadSPI
uses the Micron MT25QU256ABA, which is 256 Mb (32 MB) in size. The QuadSPI interface offers up
to 100 MHz performance for the Single Data Rate (SDR). Header J16 provides a convenient means for
energy consumption measurement. The QuadSPI is also supported by the internal Kinetis BootROM.
12. Mobile SDRAM memory
FRDM-K28F also includes a single 128 Mb mobile SDRAM memory that operates at 3.3 V. The
on-board mobile SDRAM uses the ISSI IS42SM16800H-6BLI. The SDRAM controller interface offers
performance of up to 75 MHz. Header J10 provides a convenient means for energy consumption
measurement.
13. Secure Digital (SD) card
A micro SD card slot is available on the FRDM-K28F board. It is connected to the SD Host Controller
(SDHC) signals of the MCU. This slot accepts micro SD memory cards. The SD card detect pin is an
open switch that shorts with VDD when a card is inserted. Table 6 shows the SDHC signal connection
details.
Figure 13. Micro SD card connector
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FlexIO socket
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Table 6. Micro SD card signal connections
Pin
Function
FRDM-K28F connection
P1
DAT2
PTE5/SPI1_PCS2/UART3_RX/SDHC0_D2/FTM3_CH0
P2
CD/DAT3
PTE4/LLWU_P2/SPI1_PCS0/UART3_TX/SDHC0_D3/TRACE_D0
P3
CMD
PTE3/ADC1_SE7A/SPI1_SIN/UART1_RTS/SDHC0_CMD/TRACE_D1/SPI1_SOUT
P4
VDD
3.3 V board supply (P3V3)
P5
CLK
PTE2/LLWU_P1/ADC1_SE6A/SPI1_SCK/UART1_CTS/SDHC0_DCLK/TRACE_D2
P6
VSS
Ground
P7
DAT0
PTE1/LLWU_P0/ADC1_SE5A/SPI1_SOUT/UART1_RX/SDHC0_D0/TRACE_D3/I2C1_SL/SPI1_SIN
P8
DAT1
PTE0/ADC1_SE4A/SPI1_PCS1/UART1_TX/SDHC0_D1/TRACE_CLKOUT/I2C1_SDA/RTC_CLKOUT
G1
SWITCH
PTB5
S1-S4
S1-S4
Shield ground
14. FlexIO socket
There is a 28-pin header with 20 FlexIO signals connected on the bottom of the board. It is compatible
with the MikroElektronica TFT Proto 5” capacitive touch display.
Figure 14. Accelerometer and magnetometer
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Push-button switches
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NXP Semiconductors 17
15. Reset
The reset push-button (SW1) is connected to the reset signal on the K28F MCU through a level-shifter
(U8) and to the OpenSDA v2.2 circuit. The reset button can be used to force an external reset on the
target MCU. The reset button can also be used to force the OpenSDA v2.2 circuit into the bootloader
mode. When not using the OpenSDA v2.2 circuit to supply power, the reset signal can be connected
directly to the target MCU. For more details, see Section 3.2, “Serial and Debug Adapter version 2
(OpenSDA v2.2)”.
Figure 15. Reset circuit
16. Push-button switches
Two push-buttons (SW2 and SW3) are available on the FRDM-K28F board. SW2 is connected to PTA4
and SW3 is connected to PTD0. Besides the general-purpose input/output functions, SW2 can be also
used as a Low-Leakage Wakeup (LLWU) source.
Table 7. Push-button switch connections
Switch
K28F connection
SW2
PTA4/NMI_B
SW3
PTD0/LLWU_P12
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Visible light sensor
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Figure 16. Push-button switches
17. Visible light sensor
FRDM-K28F has an on-board visible light sensor (Q5) which is connected to ADC0_SE16.
Figure 17. Visible light sensor
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Input/output connectors
Freedom Board for Kinetis K28F (FRDM-K28F), User's Guide, Rev. 0, 04/2017
NXP Semiconductors 19
18. Debug
The debug interface on the MK28FN2M0VMI15 MCU is the Serial Wire Debug (SWD) port with the
trace output capability. There are two debug interfaces on FRDM-K28F: the on-board OpenSDA v2.2
circuit (J12) and the K28F direct SWD connection via the 10-pin header (J23). To use an external
debugger (such as J-Link on J23), you may need to disconnect the OpenSDA v2.2 SWD circuit from the
K28F by removing jumpers J7 and J8.
19. Input/output connectors
The MK28FN2M0VMI15 MCU is packaged in the 169 MAPBGA package. Some pins are used in the
on-board circuitry, but some are connected directly to one of the four I/O headers (J1, J2, J3, and J4).
The pins on the K28F MCU are named after their General-Purpose Input/Output (GPIO) port pin
function. For example, the first pin on port A is referred to as PTA1. The name assigned to the I/O
connector pin corresponds to the GPIO pin of the K28F MCU.
Figure 18. FRDM-K28F I/O header pinout
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Jumper table
Freedom Board for Kinetis K28F (FRDM-K28F), User's Guide, Rev. 0, 04/2017
20 NXP Semiconductors
20. Arduino compatibility
The I/O headers on the FRDM-K28F board are compatible with the peripheral boards (known as
shields) that connect to the Arduino and Arduino-compatible MCU boards. The outer rows of pins (the
even numbered pins) on the headers share the mechanical spacing and placement with the I/O headers
on the Arduino Revision 3 (R3) standard.
21. Jumper table
The following table shows the available jumper options on the FRDM-K28F board. The default jumper
settings are shown in bold.
Table 8. FRDM-K28F jumper table
Jumper
Option
Setting
Description
J5
Reset push-button bypass
1-2
Reset button connected to OpenSDA
J7
SWD_CLK
1-2
OpenSDA SWD_CLK isolation jumper
J8
SWD_DIO
1-2
OpenSDA SWD_DIO isolation jumper
J9
OpenSDA reset
DNP*
OpenSDA reset isolation jumper (*shorted on board)
J10
SDRAM supply
DNP*
Measurement point for the SDRAM supply (*shorted on board)
J11
OpenSDA power
DNP*
Isolate the power to the OpenSDA circuit (*shorted on board)
J13
USB host
1-2
OFF host power disable
ON host power enable
J14
VBUS
1-2
USB1_VBUS isolation
J15
VDDIO_E supply
1-2
Measurement point for the K28 VDDIO_E (1.8 V) power domain
J16
QuadSPI supply
DNP*
Measurement point for the QuadSPI supply (*shorted on board)
J17
SWD_CLK
DNP*
Isolate the SWD_CLK from the SWD header (*shorted on board)
J18
VDD supply
1-2
Measurement point for the K28 VDD (1.8 V or 3.3 V) power domain
J20
VDD selection
1-2
2-3
VDD domain is 3.3 V
VDD domain is 1.8 V
J21
VBAT supply
DNP*
Isolate the VDD_VBAT (*shorted on board)
J22
VDD CORE supply
1-2
Measurement point for the K28 VDD (1.2 V) power domain
J25
5V DC support
DNP
Optional 5 V regulator
J26
P3V3_VREG protection
DNP*
Enable the diode protection when using an external supply on P3V3
(*shorted on board)
J53
USB HS and FS selection
1-2
OFF USB HS
ON USB FS
J54
USB host power selection
1-2
2-3
From the SDA circuit
From the 5 V regulator
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