NXP Semiconductors MKW01Z128, Reference Manual

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System Considerations
MKW01xxRM Reference Manual, Rev. 3, 04/2016
4-8 Freescale Semiconductor, Inc.
additional GPIOs, PTC4, and PTC3, off chip. These connections are used by applications software
in packet mode.
• At the user’s discretion, the additional DIO5:DIO2 can be connected externally to the MCU GPIO
and programmed as status indicators -
— Use of selected signals must be programmed on the transceiver
— If interrupt request (IRQ) capability is desired, any status signal must be connected to an IRQ
capable GPIO pin.
4.4.2 Transceiver Oscillator
The transceiver crystal oscillator is the main timing reference of the device. The transceiver oscillator
source must always be present and an external crystal is typically used to implement the oscillator,
although an external TCXO may also be used (see
Section 5.5.1, “Reference Oscillator” ). The source
frequency is normally 32 MHz.
In Figure 4-4 crystal Y1 and two capacitors form the transceiver crystal oscillator circuit. An off board
feedback resistor between input XTA and output XTB is not required. An important parameter for the
crystal Y1 is the load capacitance. The oscillator needs to see a balanced load capacitance at each terminal,
and as a result, the sum of the stray capacitance of the pcb board, device pin (XTA or XTB), and load
capacitor at each terminal should be equal. The amount of external load capacitance is determined by the
specific crystal specification.
NOTE
• There is no on-chip trim capacitance, therefore the user should evaluate
and size the external load capacitors to center the oscillator frequency
within the cut tolerance of the crystal.
• The frequency accuracy of the crystal (cut tolerance plus temperature
variation) must be matched to the required specification of the
application.
• To compensate for reference error, actual RF frequency can be adjusted
to the desired frequency by offsetting of the PLL control word, Frf.
4.4.2.1 Crystal Resonator Specification
Table 4-2 shows the crystal resonator specification for the crystal reference oscillator circuit of the
MKW01Z128 transceiver. This specification covers the full range of operation and is employed in the
reference design.
Table 4-2. Crystal Specification
Symbol Description Conditions Min Typ Max Unit
FXOSC XTAL Frequency 26 32 33 MHz
Rs XTAL Serial Resistance - 30 140 ohms
C0 XTAL Shunt Capacitance - 2.8 7 pF
CLOAD External Foot Capacitance On each pin XTA and XTB 8 16 22 pF