Old school 5-Tone stuff: The Auto Reset Timer

A number of MOTOTRBO models (at least in EMEA) support Select-5 signalling (a.k.a. 5-Tone).

Select-5 is one of many signaling systems used on analogue (FM) radio systems, in which transmissions consist of or include a burst of sequential audio tones. Receiving radios that are set to respond to the transmitted tone sequence will either open their squelch or carry out an action. There are several formats available (each format defines specific audio frequencies and tone duration) such as ZVEI and CCIR.

When I say open their squelch, it means that, in the quiescent state, any communications on the currently selected channel does not come through on the loudspeaker. In other words, the receiver remains squelched (or the squelch is closed).
To open the squelch and have the radio user hear the incoming transmission, you would need to send a tone sequence that matches that programmed which is programmed in the radio. This will open the squelch, in that the targeted radio will now operate using carrier or PL/DPL squelch. The radio can also sound an alert tone.

Once the squelch is opened; the message has been passed and the channel is free for other users, there needs to be a means to close the squelch again. For this, Motorola radios have a feature called Auto-Reset. There are three configuration options (modes) for Auto-Reset. Two of them start a timer that will reset the squelch once certain conditions are met.

If there was no auto-reset, the squelch would remain open once a selective call was received!

The options for auto-reset are:

If there is no carrier present on the channel for N seconds. This setting is known as Carrier Override.
N seconds after receiving the Selective Call. This setting is known as Carrier Independent.
The squelch stays open for as long as the user needs. They can close the squelch again by pressing the monitor button. This is known as Manual Override.

Auto-Reset Mode settings in the 5-Tone Channel.

In order for auto-reset to work, Auto-Reset Start (see below in yellow) needs to be enabled in the radio codeplug. This starts the timer that counts down to 0 from N. The Auto-reset Timer starts counting as soon as the Decoder Definition is triggered by a selective call.