Debugging Interface; Virtual Serial Port; Clock Source - Freescale Semiconductor FRDM-KL27Z User Manual

OpenSDA is managed by a Kinetis K20 MCU built on the ARM Cortex-M4 core. The OpenSDA circuit
includes a status LED (D8) and a RESET pushbutton (SW2). The pushbutton asserts the Reset signal to
the KL27Z target MCU. It can also be used to place the OpenSDA circuit into Bootloader mode by holding
down the RESET pushbutton while plugging the USB cable to USB connector J13. Once the OpenSDA
enters bootloader mode, other OpenSDA applications such as debug app can be programmed.
SPI and GPIO signals provide an interface to the SWD debug port of the KL27Z. Additionally, signal
connections are available to implement a UART serial channel. The OpenSDA circuit receives power
when the USB connector J13 is plugged into a USB host.
5.3

Debugging interface

Signals with SPI and GPIO capability are used to connect directly to the SWD of the KL27Z. These signals
are also brought out to a standard 10-pin (0.05") Cortex Debug connector (J11) as shown in
possible to isolate the KL27Z MCU from the OpenSDA circuit and use J11 to connect to an off-board
MCU. To accomplish this, cut the trace between pin1 and pin2 of J18 on bottom layer. This will disconnect
the SWD_CLK pin to the KL27Z so that it will interfere with the communications to an off-board MCU
connected to J11.
5.4

Virtual serial port

A serial port connection is available between the OpenSDA MCU and LPUART0 pin PTA1(TXD) and
PTA2 (RXD) of KL27Z. Several of the default OpenSDA Applications provided by Freescale, including
the MSD Flash Programmer and the P&E Debug Application, provide a USB Communications Device
Class (CDC) interface that bridges serial communications between the USB host and this serial interface
on the KL27Z.
5.5

Clock source

The Kinetis KL27 microcontrollers feature an on-chip oscillator compatible with input crystal: 32 to 40
KHz or 3 to 32 MHz. The KL27Z on the FRDM-KL27Z is clocked from the internal clock LIRC (2 MHz/8
MHz) or HIRC (48 MHz), and on-board 32768 Hz crystal for the RTC clock source.
Freescale Semiconductor, Inc.
Figure 4. SWD debug connector to KL27Z
FRDMKL27Z User's Guide, Rev. 0, 02/2015
FRDM-KL27Z hardware description
Figure 4. It is
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