TWR-KV31F120M Tower Module, User’s Guide, Rev. 0, 03/2014
6
Freescale Semiconductor Inc.
Hardware description
6.2
Clocking
Kinetis V Series MCUs start 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. An 8-MHz crystal is the default external source for the MCG oscillator inputs
(XTAL/EXTAL).
By connecting J25 (2-3) jumper enables other external clock sources for the KV31F512VLL12 include the
CLKIN0 signal, which can be provided through the TWR-ELEV module or pin 20 of TWRPI connector
J6.
6.3
System power
When installed into a Tower System, the TWR-KV31F120M can be powered from either an on-board
source or from another source in the assembled Tower System.
In stand-alone operation, the main power source (5.0 V) for the TWR-KV31F120M module is derived
from the OpenSDA USB micro-B connector (J21). Two low-dropout regulators provide 3.3 V and 1.8 V
supplies from the 5.0 V input voltage. All of the user-selectable options can be configured using two
headers, J1 and J5. Refer to sheet 4 of the TWR-KV31F120M schematics for more details.
6.4
Debug interface
There are two debug interface options provided: the on-board OpenSDA circuit and an external ARM
Cortex JTAG connector. The ARM Cortex JTAG connector (J19) is a standard 2x10-pin connector that
provides an external debugger cable access to the JTAG interface of the KV31F512VLL12. Alternatively,
the on-board OpenSDA debug interface can be used to access the debug interface of the
KV31F512VLL12.
6.4.1
OpenSDA
An on-board K20DX128VFM5-based OpenSDA circuit provides a SWD debug interface to the
KV31F512VLL12. A standard USB A male to micro-B male cable (provided) can be used for debugging
via the USB connector (J21).
The OpenSDA interface also provides a USB to serial bridge. Drivers for the OpenSDA interface are
provided in the P&E Micro OpenSDA Tower Toolkit. These drivers and more utilities can be found online
at http://www.pemicro.com/opensda.
