Channel memory
An automatic channel memory system (ACMS) is a system in which a digitally controlled
Channel scanning
A typical TV device allows an automatic channel scan to be performed from a
It now also applies to
Analog station presets and digital channel maps are normally deleted when a new scan is started. On some tuners, digital channel maps can be added-to with an "easy-add" channel scan, which is useful for finding new stations without losing old ones that may be
Many will also automatically add a new digital station's subchannels by tuning manually to the station's physical channel, though if this conflicts with the virtual channel number of another station, a complete re-scan may be the only solution. (Choosing an unused subchannel number [i.e. 30.99] on that major channel number [i.e. 30] may avoid the remap on existing subchannels [i.e. 30.1] and force the tuner to listen on that physical channel.) This has often happened in the U.S., where stations (especially
The same problem also occurs when the same station moves its digital transmission back to its old analog channel. There is no way to delete a station from the internal channel map, and a re-scan may be needed; or if the new physical channel is found, it may leave the old mapping in place, causing duplicate channels that cannot be accessed through direct entry of the numbers without also pressing the channel-up/down buttons.
Many modern TV sets do an ACMS scan automatically as part of the setup process the user is guided through when the device is initially plugged-in. While early sets often lost their memory in a