Original Site: http://www.chez.com/mickeyque/rds.htm
Since 1988, many stations of radio of tape F.M. (88 MHz - 108 MHz) emit in addition to the stereophonic audio signal, also a signal R.D.S.. Thanks to the R.D.S. (Radio Went back System = system to data transmission per radio), transmitters F.M. provide additional information concerning the program in progress. Thus stations F.M. communicate to the receivers the names of the station, the frequencies of release, the hour, the type of diffused music. Lately certain radios use this system to diffuse briefs messages texts such as advertising slogans or information for concerts and spectacles. Receivers RDS start to develop considerably in Europe (car radios, receivers mobile, minicomputer - chains, high fidelity channels and cards tuner F.M. on computer) in spite of a slight delay by report/ratio in North America.
In the case of our realization, for reasons of obvious simplifications, the demodulation is entirely carried out by an integrated circuit manufactured by the SGS-Thomson company. It is about the RDS+Filtre demodulator the TDA7330. This just component of many functions such as a capacity filter commutated of the 8 ième command centered around 57 kHz, a loop with locking of phase, an oscillator based on a quartz of 4.332 MHz suitable for the application of demodulation RDS. The following drawing shows the spectrum of the signal FM such as it must come out of the radio operator tuner. It should well be taken care that the radio operator receptor DOES NOT FILTER the signal of 20Hz with 15KHz...
This circuit of which we will not detail the operation
provided in its output several numerical signals : the clock
signal (1187.5 Hz), the signal of data RDS synchronized with the
clock, a signal of quality which indicates by a high state if the
signal received multiplexing contains or not data RDS. The data
coming out of the demodulator are represented on the chronogram below.
One period of clock is of 1/1187.5=842µS what is here the
duration of a data bit RDS. the importance of the duration of the bit
is of primary importance to carry out a correct acquisition of the
data. Moreover, the data are accessible 4.3µS after a rising
face of clock and the time of locking of the demodulator is about 100
ms after the arrival of a signal RDS. All these parameters will have
to be taken into account by our decoding routine.
The components assembled around the TDA7330 those are
specified by the manufacturer thus guaranteeing a correct operation of
the assembly. The diagram selected is thus that below east functions
trés well with card 68HC11F1 proposed on this site.
The program has of aillor written for...
The traditional components such as 68HC11 and display LCD are current. On the other hand, as an indication, the TDA7330 is available at Electronique 33 Bordeaux (Electronic diffusion) Tel.:05 56 52 14 18, the quartz of 4.332MHz is available in stock at DAHMS ELECTRONIC, 11 street Ehrman 67000 STRASBOURG. Tel.:03 88 36 14 89.
The flow charts are given below: cliquer on the images to
see them in larger.
_ Acqui1 _ Acqui2
_ Display _ Valc
_ Tempo 120µS _ Tempo 4.5 ms
The source files ASC and S-record S19 are downloadable below
while cliquant with the mulot on the link:
The program suggested functioning finally! The débuggage was begun the 18/08 and was finished the 19/08!
Small history: the program rds.asm V1.0 was written in April 1999 during the meetings of joists of
realization by the B3 group of IUT GEII of Bordeaux-Talence promo 99.
The program rds V1.0 is identical to rds
V1.1 except in the calculation of the syndrome. The first
program was based on a routine of calculation optimized in
the face memory but not of speed. It came from a program
written at the base for microcontrôleurs PIC16F84 (appeared in
Circellar). Let us recall that calculation bit by bit of the syndrome
must be carried out in less 842s (lasted of 1 bit RDS). The second
program was optimized of speed because the loop of
calculation of the syndrome " was unrolled ". This alternative comes
from the scope note of Motorola an460.pdf.
The last versions (V2.x) proposed on the site go finally trés well and the calculation of syndrome A was improved by the use of all the registers of the 68HC11. The routine of the calculation of the syndrome comes from the scope note an495.pdf. It is about a scope note available on the site of MOTOROLA probably since in May-Juin99 and which proposes a decoder RDS with a 68HC11 (see the lower links for the address).
The programes V2.x are adapted to function on card 68HC11F1 in extend mode with PCBUG11 v3.42. Version 2.3 manages for the moment pi codes (identifying station), the PS name (the name of the station), the Music/Speech indicator, the PTY (standard of program), the hour and RadioTexte. The development of the rolling programme and will propose the management of the traffic road, the PINE (Program Item Number, similar to system PDC for the video tape recorders) as well as other information intérraissantes...
The image below accurately reproduced the display of decoder RDS V2.3: on the first line on the left the name of the station (PSname: 8 characters received per pair) on the right the hour of the station (raffraichi every minute). Then on the second line, there are 2 views:
- no pressure on SW1: on the left pi codes station (trés useful for débugger!), in the medium the Musique/Parole indicator (trés seldom used) and on the right TYpe de Programme (PTY: style of the station: Rock'n'roll, Information, Sport, Music, varieties...).
- a pressure on SW1: run of the message RadioTexte (64 characters) aprés its complete reception (approximately maximum 15s aprés reception of a station which diffuses RadioTexte). Aprés the run of the message, information PTY and pi code are réaffichées. The support again on SW1 again causes the run of the Radio operator Text. If the station does not diffuse RadioTexte or well if the message is not completely received, the display will not be modified.
The team thanks the malls which were addressed to take part in the débuggage by éclaicissant the principle of the decoding of the syndrome. Thanks particular to FP for the sources and the explanations!