TWR-K70F120M Tower Module User's Manual Page 10 of 25
SPI, I2C (w/ SMBUS support), UART (w/ ISO7816, CEA709.1-B (LON), and IrDA support), CAN, I2S
SD Host Controller (SDHC)
GPIO with pin interrupt support, DMA request capability, digital glitch filtering
Capacitive touch sensing inputs (TSI)
Debug interfaces: JTAG, cJTAG, SWD
Trace: TPIO, FPB, DWT, ITM, ETM, ETB
2.2 Clocking
The Kinetis MCUs start up from an internal digitally controlled oscillator (DCO). Software can enable
one, two, or three external oscillators if desired. Two of the external oscillators provide clocks to the
Multipurpose Clock Generator (MCG) module and can range from 32.768 KHz up to a 32 MHz crystal or
ceramic resonator. The external oscillator for the Real Time Clock (RTC) module accepts a 32.768 kHz
crystal.
The EXTAL0 and EXTAL1 pins of the main external oscillators can also be driven directly from an
external clock source. The TWR-K70F120M features a 50 MHz on-board clock oscillator connected to
EXTAL0 as seen in sheet 4 of the schematics. However, when the K70 Ethernet MAC is operating in
RMII mode, synchronization of the MCU input clock and the 50 MHz RMII transfer clock is important.
In this mode, the MCU input clock must be kept in phase with the 50 MHz clock supplied to the
external PHY. Therefore, the TWR-K70F120M provides the option (see jumper description in Table 5)
to select the clock input to the MCU from 1) the on-board 50MHz source or 2) an external clock from
the CLKIN0 pin on the Primary Connector. When the K70 is operating in Ethernet RMII mode, the
Tower peripheral module implementing the RMII PHY device should drive a 50 MHz clock on the
CLKIN0 signal that is kept in phase with the clock supplied to the RMII PHY. Refer to section 2.13
“Ethernet” for more information.
The TWR-K70F120M also includes a 12MHz crystal connected to EXTAL1/XTAL1.
2.3 System Power
In stand-alone operation, the main power source for the TWR-K70F120M module is derived from the
5.0V input from either the USB mini-B connector, J13, or the debug header, J11, when a shunt is placed
on jumper J12. A low-dropout regulator provides a 3.3V supply from the 5.0V input voltage. Refer to
sheet 6 of the TWR-K70F120M schematics for more details.
When installed into a Tower System, the TWR-K70F120M can be powered from either an on-board
source or from another source in the assembled Tower System. If both the on-board and off-board
sources are available, the TWR-K70F120M will default to the off-board source.
The 3.3V power supplied to the MCU is routed through two jumpers, J8 and J20. J8 can be supplies
VDD to the processor and also VDD_INT as long as J20 is installed. J20 supplies VDD_INT to the
processor. The jumper shunts can be removed to allow for either 1) alternate MCU supply voltages to
be injected or 2) the measurement of power consumed by the MCU.