2002 Jan 14 10
Philips Semiconductors Product specification
RDS/RBDS pre-processor SAA6588
The input of the pause detector (AFIN) is low-ohmic and
must be current driven (negative input of an operational
amplifier). This has the following advantages:
• One (MPX) as well as two (left and right) AF channel
application is possible and requires only one pin
• Unwanted crosstalk is avoided if two AF channel
application is chosen
• Matching the input sensitivity is possible by external
resistors.
For combined application (RDS and AMS) variations of the
switching threshold level as well as the minimum time for
pause detection are possible via I
2
C-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=5kΩ; for 2 channels: R = 10 kΩ).
The corresponding values of FM deviation are calculated
for stereo decoders with an output voltage of 270 mV at
22.5 kHz deviation.
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.
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).
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.
According to the used oscillator frequency, the mode
control bits PTF1, PTF0 and SOSC have to be set via the
I
2
C-bus after every reset, see Section “Programming”
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
⁄
2
V
DDA
) is
internally generated and available via the output pin V
ref
.
The I
2
C-bus interface requires a defined reset condition.
The pre-processor generates a reset signal:
• After the supply voltage V
DDD
is switched on
• At a supply voltage drop
• If the oscillator frequency is lower than 400 Hz.
This internal reset initializes the I
2
C-bus interface registers
as well as the I
2
C-bus slave control and releases the data
line SDA (SDA = HIGH) for input of control mode settings
from the main controller.
If the decoder detects a reset condition, the status
information ‘reset detected’ (RSTD) is set and available via
I
2
C-bus request. The RSTD flag is deactivated after the
decoder status register was read by the I
2
C-bus. This
status information is important to signal the main controller
about a voltage drop in the pre-processor IC.
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.
Programming
I
2
C-BUS SLAVE TRANSCEIVER
For communication with the external main controller
(master transceiver) the standard I
2
C-bus is used.
The pre-processors I
2
C-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).
The I
2
C-bus interface is connected to the external I
2
C-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.
