NXP Semiconductors MKW01Z128, Reference Manual, Page: 46 / 884

System Considerations
MKW01xxRM Reference Manual, Rev. 3, 04/2016
Freescale Semiconductor, Inc. 4-9
NOTE
• The initial frequency tolerance (cut tolerance), temperature stability and
aging performance should be chosen in accordance with the target
operating temperature range and the receiver bandwidth selected.
• The loading capacitance should be applied externally, and adapted to the
actual C
load
specification of the crystal.
• A minimum crystal frequency of 28 MHz is required to cover the
863-870 MHz band and 29 MHz for the 902-928 MHz band.
4.4.2.2 Transceiver ClkOut Output (DIO5)
The reference frequency, or a fraction of it, can be provided as an output on DIO5. Use of the ClkOut
output allows:
• Driving the clock source to the MCU -
— Saves the cost of an additional crystal.
— ClkOut can be made available in any operation mode except Sleep mode and is automatically
enabled at power-on reset.
• Trimming of the reference oscillator frequency - ClkOut can be provided as a test point for a
frequency counter to allow trimming of the external load capacitance during design/evaluation.
The ClkOut functionality is controlled by programming transceiver Register RegDioMapping2 (0x26)
(see
Section 7.10, “IRQ and Pin Mapping Registers” ):
• Bits 5:4 - control the function of DIO5 and enable ClkOut. See Table 7-2 and Table 7-3.
• Bits 2:0 - control the ClkOut frequency.
Table 4-3 lists ClkOut frequency versus Bits 2:0 setting using a 32 MHz reference source.
Table 4-3. ClkOut Frequency Using 32 MHz Reference Oscillator
ClkOut
Bits 2:0
Divide
Ratio
ClkOut Frequency
(MHz)
000 1 32
001 1/2 16
010 1/4 8
011 1/8 4
100 1/16 2
101 1/32 1
110 RC 62.5 kHz
(Automatically enabled)
111 - OFF