In the fire detection industry, analogue addressable systems use control panels and detectors (and devices such as interfaces) which communicate with each other by means of a protocol.

What protocol is this?

Analogue addressable system diagram

Can anyone help me find information about it?

  • \$\begingroup\$ Honeywell defined such a protocol, decades ago. About 20 volt signaling, on an 80 volt DC power rail. All this from memory. \$\endgroup\$ – analogsystemsrf Oct 23 '18 at 17:58

What protocol is used is impossible to say unless I have access to the technical documentation of the units and/or can reverse-engineer them.

We can assume that it is some kind of communication protocol suitable for one shared connection (no separate TX, RX, clock etc. but one bidirectional signal).

With some electronics it is possible to make data and power share the same pair of wires. This is nothing new, the old wired telephone system already used it!

Here are some links that show how this can be done:

Transmit Digital Signals and Power Over Same Wires

Using SN65HVD96 to Create a Power-Over-Data and Polarity Immunity Solution

The basic idea is that the power is DC and the data is AC. With some electronics (that can be as simple as an RC filter or a transformer) the two (data, power) can be combined and separated in each device.

  • \$\begingroup\$ Thanks for your share. It's a useful information for me \$\endgroup\$ – VirtueVu Oct 23 '18 at 10:17

I studied the technologies about how to transmit data and power on two-wire and found an answer for this issue.

The result of study show that analog 4–20 mA current loops are commonly used for electronic signalling, with the two values of 4 & 20 mA representing 0–100% of the range of measurement or control. These loops are used both for carrying sensor information from field instrumentation, and carrying control signals to the process modulating devices, such as a valve In the case of a fire alarm, 6 mA could be normal, 15 mA could mean a fire has been detected, and 0 mA would produce a trouble indication, telling the monitoring site the alarm circuit had failed.

Some 4–20 mA field devices can be powered by the current loop itself, removing the need for separate power supplies, and the "smart" HART protocol uses the loop for communications between field devices and controllers. Here are some links:



However, I haven't make sure that the addressable fire alarm Systems are using. Can anyone help me confirm that this is right or wrong?


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