Editing Radio Data System (section)

=={{anchor|AF|CT|EON}}Content and implementation==
[[File:TomTom Navigation System with RDS-TMC.jpg|thumb|A Radio Data System – Traffic Message Channel (RDS-TMC) receiver (left) attached to a [[TomTom]] navigation system to integrate real-time traffic data into the navigation.<ref>{{cite web|title=Traffic Receiver|url=http://www.tomtom.com/en_gb/products/your-drive/accessories/most-popular/traffic-receiver-9UUC.002.00.2/|publisher=TomTom|access-date=15 June 2014}}</ref>]]
[[File:RDS en la app Radio FM de un Smartphone Samsung.jpg|thumb|250x250px|Radio Data System display of an FM Radio station from Spain.]]
The following information fields are normally contained in the RDS data:
;AF ([[Alternative frequency|alternative frequencies]] list): This provides the receiver with a list of frequencies that allows a receiver to re-tune to a different [[radio frequency|frequency]] providing the same [[radio station|station]] when the first signal becomes too weak (e.g., when moving out of range). Before performing the switch, a radio will check for a matching PI code to ensure the AF is the same station. This is often used in car stereo systems, allowing the head unit to automatically tune into the stronger signal on the move, optionally with the same regional code (so that, in the case of national broadcasting stations, the user can keep listening to the original radio program).
;CT (clock time and date): 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&nbsp;ms of [[UTC]]. CT is not usually transmitted if a broadcaster has no way to regularly synchronise the clock within the RDS encoder.
;EON ([[enhanced other networks]] information): Informs the receiver about other networks or stations, linked to the one being listened to, for dynamically changing data such as the TA flag turning on for a particular station of the network in a particular moment due to a [[traffic]] [[Traffic reporting|programme]] being broadcast, and automatically and temporarily allows the radio to tune into that station.
;PI ([[programme identification]]):This is the unique 4 character [[hexadecimal]] code that identifies the station. Every station in a country should use a unique 3 character code with the correct country prefix character. In the US, PI is determined by applying a formula to the station's [[call sign]], or randomly assigned by the [[National Radio Systems Committee|NRSC]] to FM translators (which have a longer call sign, making them incompatible with the formula).<ref>{{Cite web|last=Jurison|first=Alan |date=28 November 2017|title=NRSC Activates PI Codes for FM Translators Web Resource|url=https://nabpilot.org/nrsc-activates-pi-codes-for-fm-translators-web-resource/|website=NAB Pilot|access-date=2020-09-17}}</ref> The PI code is the most important RDS parameter and the most frequently transmitted within the RDS data structure. The RDS standard for non US use defines country codes for all countries so that nowhere with common borders has the same code. This removes the need to coordinate PI codes between different countries. Any transmission that carries the same code is considered by receivers to be the same and can be switched to as an alternative frequency to improve reception (even if it is not specifically listed as an alternative frequency). PI codes can be generically linked. A PI code is generically linked if the first, third and fourth nibbles are the same. Generic linking is typically done by radio stations in different areas that are related in some way. Receivers (especially those in vehicles) may have a setting called 'Regional' which when activated allows the radio to switch to another generically linked station. PI codes are normally static (i.e. do not change). However, in the UK some networks use dynamic PI codes where the second nibble changes (to a generically linked code). The national broadcaster Classic FM for example does this. The intention of this is to prevent radios retuning during commercial breaks where each transmitter carries a different set of commercials.

;PS (programme service name): 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 PI code, frequency and other details associated with that preset. In some countries, stations use the PS to dynamically send other information. This is prohibited in some countries and was not its intended use within the RDS system.
;PTY (programme type): This coding of up to 31 pre-defined programme types (e.g., in Europe: PTY1 News, PTY6 Drama, PTY11 Rock music) allows users to find similar programming by genre. PTY31 is reserved for emergency announcements in the event of natural disasters or other major calamities.
;REG (regional): This is mainly used in countries where national broadcasters run "region-specific" programming such as regional opt-outs 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. See the description of Program identification code below for further information.[[File:Radio Data System (RDS) on 95.9 KFSH La Mirada.jpg|thumb|261x261px|An example of RT RDS on Los Angeles' [[KFSH-FM]]]]
;RT (radio text): This function allows a radio station to transmit a 64 (or less commonly 32) character free-form text message 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). 
;RT+ (radio text plus): An enhancement of the original RT which allows Artist, Title and some other metadata to be sent to receivers.
;TA, TP ([[Traffic Announcement|traffic announcement]], traffic programme):The receiver can often be set to pay special attention to this flag (taking advantage of the EON linkage if it's available) and, for example, pause a 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 pausing a CD/MP3 (so the radio can be heard) or raising the volume during the traffic bulletin.
;TMC ([[Traffic Message Channel|traffic message channel]]): Digitally encoded traffic information. Not all RDS equipment supports this, but it is often available for [[automotive navigation system]]s. 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. The subscription is often paid by the vehicle manufacturer and is therefore transparent to the user.
;US NRSC FM Translator Announcements: The National Radio Systems Committee has introduced a unique Radio Data System Program Identification code for US FM translators. One type of metadata transmitted by RDS subcarrier is the PI code, which is used by the receiver to uniquely identify the audio program being broadcast by the FM station. In the U.S., the PI code has historically been derived from a radio station's call sign, which can become complicated when used in conjunction with FM translators. A new algorithm just for FM translators has been created that assigns a unique PI code to each FM translator. This algorithm has been implemented using a web-based tool and a list of all known PI codes for all FM translators in the US. [http://picodes.nrscstandards.org/]