AN2294 Freescale Semiconductor / Motorola, AN2294 Datasheet - Page 3

• Manufacturer Part Number: AN2294
• Description: MC68SZ328 USB Configuration Setup Application Note
• Manufacturer: Freescale Semiconductor / Motorola

Components R313, C252, R314 and C253 are not installed normally, they serve the purpose of fine tuning
the circuit.
2.3 USB Crystal Configuration
The USB uses its own stand-alone crystal that is isolated from the MCU PLL. Its function is to provide the
necessary clock signal to run the USB (48 MHz). Both the MCU PLL and the USB PLL clock frequencies
can be programmed using Equation 1 on page 5. The values for UMFI, UMFN, UMFD, and UPDF are
programmable using the UPFSR0 and UPFSR1 registers. Detailed information about these registers can be
found in the MC68SZ328 Reference Manual (Chapter 5). Figure 2 illustrates the crystal configuration
hardware for a 32.768 kHz crystal, and Figure 3 on page 4 illustrates the crystal configuration hardware for
the 16 MHz crystal.
MOTOROLA
Figure 1. Connection From MC68SZ328 to the Transceiver Using USB Outputs
Figure 2. 32.768 kHz Crystal Configuration Hardware
Freescale Semiconductor, Inc.
For More Information On This Product,
MC68SZ328 Application Note
Go to: www.freescale.com
CLK32KI
CLK32KO
Hardware Interface
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