BCM88335 Data Sheet
Frequency Selection
Frequency Selection
Any frequency within the ranges specified for the crystal and TCXO reference may be used. These include not
only the standard mobile platform reference frequencies of 19.2, 19.8, 24, 26, 33.6, 37.4, and 38.4 MHz, but
also other frequencies in this range with an approximate resolution of 80 Hz. The BCM88335 must have the
reference frequency set correctly in order for any of the UART or PCM interfaces to function correctly, since all
bit timing is derived from the reference frequency.
Note: The fractional-N synthesizer can support many reference frequencies. However, frequencies
other than the default require support to be added in the driver plus additional, extensive system
testing. Contact Broadcom for details.
The reference frequency for the BCM88335 may be set in the following ways:
•
Set the xtalfreq=xxxxx parameter in the nvram.txt file (used to load the driver) to correctly match the crystal
frequency.
•
Autodetect any of the standard handset reference frequencies using an external LPO clock.
For applications where the reference frequency is one of the standard frequencies commonly used, the
BCM88335 automatically detects the reference frequency and programs itself to the correct reference
frequency. In order for automatic frequency detection to work correctly, the BCM88335 must have a valid and
stable 32.768 kHz LPO clock that meets the requirements listed in Table 3 on page 30 and is present during
power-on reset.
Broadcom®
September 23, 2015 • 88335-DS100-R
Page 29
BROADCOM CONFIDENTIAL
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