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Philips Semiconductors
User Manual of High-End RDS/EON
Car Radio System CCR612 (V0.3)
Application Note
96029
When AF follow mode is on, the next actions are taken:
1. When selecting a preset, the radio will load the AF list from NVM, and measure the signal strength
of the primary frequency and all alternative frequencies. It will then select the strongest station with
the correct PI code, before the radio is de-muted.
(PI codes are compared with the value stored in the preset data in NVM.)
If no station with the correct PI code is found, after 6 seconds the radio will start a search tuning for
a station with the correct PI code. If still not found, it will accept the new station, but it will not update
the PI code stored in NVM.
Search tuning can be cancelledby switching AF follow mode off orby pressing the AUTO / MANUAL
key. The radio will then return to the original frequency.
2. At regular intervals - depending on the signal strength of the current station - the signal strength of
alternative frequencies ismeasured. The intervalvaries from appr. 80seconds when the signallevel
of the current station is very strong to appr. 3 seconds when it is very weak.
3. When for a certain time an AF is stronger than the current frequency, or when the current frequency
becomes suddenly unacceptable e.g. due to multipath, the radio switches to the best alternative
frequency.
When the programme service is left (by tuning, band switching or by turning the radio off), the new
frequency is stored in NVM as the primary frequency for that preset.
The AF follow algorithm has provisions for special circumstances such as:
- Mountains andbuildings. All signalstrengths vary rapidly dueto multipath distortion.Switch when
the multipath distortion level becomes unacceptable.
- Loss of RDS data or station changes PI code. Select an alternative frequency with correct PI
code.
The "quality" of a station is a value that is based on signal level as well as multipath level read from
the TEA6822 by means of the I
2
C-bus.
7.6 EON preset update
When the tuned station transmits EON information, the alternative frequencies stored for the station
presets are updated via EON. Only those alternative frequency lists of station presets can be updated
whose PI codes match one of the PI codes transmitted via EON. Whether or not regional variants of the
PI code are taken into account depends on the status of the regional selection. If the regional selection
is switched on, the transmitted PI code must exactly match the PI code to update.
If after travelling any distance while tuned to a programme service, a user selects a preset for another
station which is cross-referenced by EON-information, CCR612 has to find an acceptable frequency for
the new selected station in the new area, without resorting to a PI search. This should occur regardless
of the distance travelled, assuming of course that the station is transmitted in the new area.
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