tea5766uk NXP Semiconductors, tea5766uk Datasheet - Page 28

• Manufacturer Part Number: tea5766uk
• Description: Tea5766uk Stereo Fm Radio + Rds
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TEA5766UK_1
Product data sheet
9.4.1 Conditions for synchronization
9.4 Synchronization
When the RDS decoder is turned on it must be synchronized to extract valid data from the
MPX signal. To do so the decoder automatically initiates a search for synchronization. The
conditions to meet synchronization and the status of this synchronization can be set and
checked with the following bits:
When the decoder is not synchronized it will initiate a synchronization search. This
involves calculation of the syndrome (see EN 62106 Specification of the radio data system
(RDS) for VHF/FM sound broadcasting range from 87.5 to 108 MHz, 1998 for details) for
each block of 26 received bits on a bit-by-bit basis. When a correct syndrome (and hence
block ID) is received the decoder clocks the next 26 bits into the internal registers and
performs a second syndrome check. Synchronization is found when a certain number of
blocks have been decoded and two goods blocks have been found; this number of blocks
is defined by the BBG bits. If the first block needed for synchronization has been found
and the expected second block (after 26 bits) is an invalid block, then the decoder module
internal bad_blocks_counter is incremented and the next expected block is calculated.
Exception: if RBDS mode is selected and the first block is E, then the next expected block
is always block A, until synchronization is found or the maximum bad_blocks_counter
value is reached. If the decoder module internal bad_blocks_counter reaches the value of
the BBG[4:0], then immediately a new synchronization search (bit-by-bit) is started to find
a new first block.
The synchronization is monitored by use of two flywheel counters; GBC and BBC. These
are 6-bit counters that can be preset by the GBL and BBL bits to values between 0 and
63. Each time a block is decoded and recognized as a bad block the BBC value is
incremented by 1. When the BBC value is equal to the BBL value, synchronization is lost.
The SYNC bit will become logic 0 and the LSYNCFL is set to signal the loss of
synchronization. The TEA5766UK will now automatically initiate a new synchronization
search.
Each time when a good block is decoded the GBC value is incremented. When the GBC
value is equal to the GBL value both counters (BBC and GBC), are set to 0 and a new
count starts. The GBC counter is only incremented when the decoder is synchronized.
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BBL[5:0] - Bad Blocks Lose - these bits can be set via the bus and have a value
between 0 and 63.
GBL[5:0] - Good Blocks Lose - these bits can be set via the bus and have a value
between 0 and 63.
BBG[4:0] - Bad Blocks Gain - these bits can be set via the bus and have a value
between 0 and 32.
GBC[5:0] - Good Block Count - these bits can be read via the bus and have a value
between 0 and 63.
BBC[5:0] - Bad Block Count - bits can be read via the bus and have a value between
0 and 63.
Rev. 01 — 22 March 2007
TEA5766UK
Stereo FM radio + RDS
© NXP B.V. 2007. All rights reserved.
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