The RDS specification details a number "features" that the RDS should comply with eg: send the transmitter call sign
The following information fields are normally contained in the RDS data:
AF (alternative frequencies)
This allows a receiver to re-tune to a different frequency providing the same station when the first signal becomes too weak (e.g., when moving out of range). This is often used in car stereo systems.
CT (clock time)
Can synchronize a clock in the receiver or the main clock in a car. Due to transmission vagaries, CT can only be accurate to within 100 ms of UTC.
EON (enhanced other networks)
Allows the receiver to monitor other networks or stations for traffic programmes, and automatically temporarily tune into that station.
PI (programme identification)
This is the unique code that identifies the station. Every station receives a specific code with a country prefix. In the US, PI is determined by applying a formula to the station's call sign.
PS (programme service)
This is simply an eight-character static display that represents the call letters or station identity name. Most RDS capable receivers display this information and, if the station is stored in the receiver's presets, will cache this information with the frequency and other details associated with that preset.
PTY (programme type)
This coding of up to 31 pre-defined programme types (eg: in Europe: PTY1 News, PTY6 Drama, PTY11 Rock music) allows users to find similar programming by genre. PTY31 seems to be reserved for emergency information in the event of natural disasters or other major calamities.
This is mainly used in countries where national broadcasters run "region-specific" programming such as regional opt-out on some of their transmitters. This functionality allows the user to "lock-down" the set to their current region or let the radio tune into other region-specific programming as they move into the other region.
RT (radio text)
This function allows a radio station to transmit a 64-character free-form text that can be either static (such as station slogans) or in sync with the programming (such as the title and artist of the currently playing song).
TA, TP (traffic information, traffic programme)
The receiver can often be set to pay special attention to this flag and, for example, stop the tape/pause the CD or retune to receive a traffic bulletin. The TP flag is used to allow the user to find only those stations that regularly broadcast traffic bulletins whereas the TA flag is used to signal an actual traffic bulletin in progress, with radio units perhaps performing other actions such as stopping a cassette tape (so the radio can be heard) or raising the volume during the traffic bulletin.
TMC (traffic message channel)
Digitally encoded traffic information. Not all RDS equipment supports this, but it is often available for automotive navigation systems. In many countries only encrypted traffic data is broadcast, and so an appropriate decoder, possibly tied to a subscription service, is required to use the traffic data.
Other features include a user channel that can be used to transmit serial data (very slow) for internal use by the broadcaster or equipment manufacturer.