Philips Semiconductors
Product specification
RDS/RBDS pre-processor
SAA6588
• One (MPX) as well as two (left and right) AF channel
application is possible and requires only one pin
The I2C-bus interface requires a defined reset condition.
The pre-processor generates a reset signal:
• Unwanted crosstalk is avoided if two AF channel
application is chosen
• After the supply voltage VDDD is switched on
• At a supply voltage-drop
• Matching the input sensitivity is possible by external
resistors.
• If the oscillator frequency is lower than 400 Hz.
This internal reset initializes the I2C-bus interface registers
as well as the I2C-bus slave control and releases the data
line SDA (SDA = HIGH) for input of control mode settings
from the main controller.
For combined application (RDS and AMS) variations of the
switching threshold level as well as the minimum time for
pause detection are possible via I2C-bus control.
The level can be adjusted in four steps of 4 dB by the
control bits PL0 and PL1, see Table 8 (for 1 channel:
R = 5 kΩ; for 2 channels: R = 10 kΩ).
If the decoder detects a reset condition, the status
information ‘reset detected’ (RSTD) is set and available via
I2C-bus request. The RSTD flag is deactivated after the
decoder status register was read by the I2C-bus. This
status information is important to signal the main controller
about a voltage-drop in the pre-processor IC.
The corresponding values of FM deviation are calculated
for stereo decoders with an output voltage of 270 mV at
22.5 kHz deviation.
By default, the bits in the write registers (except bit SOSC)
are set to the values in Table 11. If these values are the
required values, no further initialization is necessary.
The minimum time for detecting a pause can be adjusted
by the control bits SOSC, PTF0 and PTF1, see Table 9.
The minimum time for detecting ‘no pause’ is fixed to 5 ms
to avoid interruptions of a pause by a short pulse.
Programming
The output signal of the pause detector is a digital
switching signal (active LOW). It is directly available via the
output pin PSWN. A detected pause may initiate an AF
search if required (FM mode).
I2C-BUS SLAVE TRANSCEIVER
For communication with the external main controller
(master transceiver) the standard I2C-bus is used.
The pre-processors I2C-bus interface acts as a slave
transceiver with fast mode option, that allows a transfer bit
rate up to 400 kbits/s but is also capable of operating at
lower rates (≤100 kbits/s).
Oscillator and clock
For good performance of the band-pass and demodulator
stages, the pre-processor requires a crystal oscillator with
a frequency of n × 4.332 MHz. The pre-processor can be
operated with one of four different oscillator frequencies
(n = 1 to 4). The 17.328 MHz frequency (n = 4) is also
UART interface compatible for 8051 based
microcontrollers with a 9600 baud rate (frequency
error = 4.5%), so that a radio set with microcontroller can
run in this case with one crystal only. The pre-processor
oscillator can drive the microcontroller or vice versa.
The I2C-bus interface is connected to the external I2C-bus
via the serial clock line SCL and the serial data line SDA.
The clock line is supplied by the master and is only input
for the slave transceiver. The data line is a serial 8-bit
oriented bidirectional data transfer line, and acts as input
for control mode settings from the main controller to the
pre-processor, as output for requested RDS/RBDS data
from the pre-processor to the main controller and
acknowledge between pre-processor and main controller.
According to the used oscillator frequency, the mode
control bits PTF1, PTF0 and SOSC have to be set via the
I2C-bus after every reset, see Section “Programming”
The transfer of requested data to the main controller is
synchronized via the additional data available output
signal DAVN to avoid loss of RDS/RBDS data. The DAVN
signal is activated if the pre-processor has provided new
data information for the main controller (see Section
“RDS/RBDS data output”) and can be used for the polling
mode as well as for the interrupt mode of the main
microcontroller.
The clock generator circuitry generates hereof the
internally used 4.332 MHz system clock and further
derived timing signals.
Power supply and reset
The pre-processor has separate power supply inputs for
the digital and analog parts of the device. For the analog
functions an additional reference voltage (1⁄2VDDA) is
internally generated and available via the output pin Vref.
1997 Sep 01
10
NXP [ NXP ]
