BCM89071A1CUBXGT Datasheet, PDF (39/69 Pages) Cypress Semiconductor – Single-Chip Automotive Grade Bluetooth Transceiver and Baseband Processor

BCM89071 Data Sheet
Frequency Selection
Frequency Selection
Any frequency within the range specified for the crystal and TCXO reference can be used. These frequencies
include standard handset reference frequencies (12, 13, 14.4, 15.36, 16.2, 16.8, 18, 19.2, 19.44, 19.68, 19.8,
20, 24, 26, 33.6, 37.4, and 38.4 MHz) and any frequency between these reference frequencies, as desired by
the system designer. Since bit timing is derived from the reference frequency, the BCM89071 must have the
reference frequency set correctly in order for the UART and PCM interfaces to function properly.
The BCM89071 reference frequency can be set in one of three ways.
• Use the default 20 MHz frequency
• Designate the reference frequency in external NVRAM
• Auto-detect the standard handset reference frequencies using an external LPO clock
The BCM89071 is set to a default frequency of 20 MHz at the factory. For a typical design using a crystal, it is
recommended that the default frequency be used, since this simplifies the design by removing the need for
either external NVRAM or external LPO clock.
If the application requires a frequency other than the default, the value can be stored in an external NVRAM.
Programming the reference frequency in NVRAM provides the maximum flexibility in the selection of the
reference frequency, since any frequency within the specified range for crystal and external frequency reference
can be used. During power-on reset (POR), the device downloads the parameter settings stored in NVRAM,
which can be programmed to include the reference frequency and frequency trim values. Typically, this is how
a PC Bluetooth application is configured.
For applications such as handsets and portable smart communication devices, where the reference frequency
is one of the standard frequencies commonly used, the BCM89071 automatically detects the reference
frequency and programs itself to the correct reference frequency. In order for auto-frequency detection to work
properly, the BCM89071 must have a valid and stable 32.768 kHz external LPO clock present during POR. This
eliminates the need for NVRAM in applications where the external LPO clock is available and an external
NVRAM is typically not used.
Broadcom^®
April 16, 2015 • 89071-DS106-R
Baseband Transceiver and Baseband Processor
Page 38