TWR-KL28Z Hardware Description
TWR-
KL28Z User’s Guide, Rev. 0, 06/2016
NXP Semiconductors
5
4.2. Serial and debug adapter (CMSIS-DAP)
CMSIS –DAP is an open-standard serial and debug adapter. It bridges serial and debug communications
between a USB host and an embedded target processor as shown in
Figure 4
. CMSIS-DAP features a
mass storage device (MSD) bootloader, which provides a quick and easy mechanism for loading
different CMSIS-DAP Applications such as flash programmers, run-control debug interfaces, serial-to-
USB converters, and more. Two or more CMSIS-DAP applications can run simultaneously. For
example, run-control debug application and serial-to-USB converter runs in parallel to provide a virtual
COM communication interface while allowing code debugging via CMSIS-DAP with just single USB
connection. These two applications are provided in a single code package. Refer to the CMSIS-DAP
User’s Guide for more details.
Figure 4. CMSIS-DAP block diagram
CMSIS-DAP is managed by a Kinetis K20 MCU built on the ARM Cortex-M4 core. The CMSIS-DAP
circuit includes a status LED (D1) and a RESET pushbutton (SW1). The pushbutton asserts the Reset
signal to the KL28Z target MCU. It can also be used to place the CMSIS-DAP circuit into bootloader
mode by holding down the RESET pushbutton while plugging the USB cable to USB connector J13.
Once the CMSIS-DAP enters bootloader mode, other CMSIS-DAP applications such as debug app can
be programmed. SPI and GPIO signals provide an interface to the SWD debug port of the KL28Z.
Additionally, signal connections are available to implement a UART serial channel. The CMSIS-DAP
circuit receives power when the USB connector is plugged into a USB host.
4.2.1. Debugging interface
Signals with SPI and GPIO capability are used to connect directly to the SWD of the KL28Z. These
signals are also brought out to a standard 10-pin Cortex Debug connector (J30) as shown in
Figure 5
. In
order to isolate the KL28Z MCU from the CMSIS-DAP circuit and use J30 to connect to an off-board
