RDS decoder IC data

[dr pepper]

I pulled a LC72725NM chip out of a car radio, its a RDS decoder, it takes the radio's IF signal and decodes RDS data from the received 57khz subcarrier.
Using my salae logic analyser I can 'see' comms from the set's micro to and from the device, so I have some idea what registers do what.
Naturally though I'd like a list of registers and how to set the device up via I2C, there are a few datasheets for this device, samsung & onsemi are a couple, however none have a register map, searching for a application datasheet or programming datasheet doesnt pull any replies.
I spose its a long shot, but any advice on where to look, or should I look for another chip.

 

[KlausST]

Hi,

according this document: https://www.ukwtv.de/cms/files/artikel/RDS-Grundlagen.pdf (German)
the RDS sends data with 1187.5 Baud
4 blocks of 26 bits each

I guess the chip sends these data without using registers, without addressing.

Klaus

 

[dr pepper]

Ah ok then I get that, I was expecting this register for this data and that register for that data, as in the Si4307 or Rda5807 devices (I think so anyway).

I'll check that during my next lab session, I'll monitor the data flow when the sets running, in fact I recall there was a read from address 0x40, and a load of data was dumped as a reply, maybe as you imply its the entire rds data dump, I can copy that to memory & bit crunch it for the data I need, the link was dead but I found a Bbc article explaining the Rds data.

Thanks.

 

[KlausST]

Hi,

sorry for the dead link.
I repaired it. It´s working now.

Klaus

 

[dr pepper]

Ok so I have some direction.
Rds data is sent in blocks, between 2 and 4 blocks, unfortunately the only way to sync is through CRC.
The decoder chip just receives the datastream and presents it as an unsync'd 128 bit buffer of data.
There is an arduino library, a spin off from a full blown Fm receiver program that will decode the Rds data and place it in its respective message registers, as I was eluding to earlier.
The thinking I'd have to do here though is syncing and CRC'ing the data, as this lib requires the Rds data blocks in sync, 1,2, 1,2,3,4 etc.
Shouldn't be that hard, I cant remember when I last looked at CRC checking.