Detecting a blown bulb - key input MIA

Well, actually, wireless units have an MMI-like mechanism that goes on. Its not exactly the same. In fact, its quite different in many reepects.

But the end result is that units continually chat amongst themselves (at ever decreasing intervals) to confirm the state of a group.

There is however nothing that mashes all that up and says "ooh this unit is not there any more".

The gateway watches all the chatter and uses this to internally build a network model of what is happening in wireless-land. It then takes MMI requests that come in from the wired side (in the form of "hey you do an MMI for me and tell me the results"). It sees that request come in, and then fakes up a bunch of replies from its internal wireless network model.

So as far as the wired side is concerned, it looks like there is an MMI being done. In fact, its a little bit of smoke and mirrors.

And again, this model does not age-out a unit so it it can't see a unit stop chattering and then remove it from the MMI reports. As far as the gateway is concerned, once seen, a unit continues to exist. UNLESS you explicitly talk directly to that unit and that unit alone and this fails, in which cases in some circumstances that unit address can become removed from the model. This is not foolproof though and cannot be relied upon.

 

Let c-gate do it.

Wireless is not designed for polling, which is what you are trying to do. You are far more likely to have false alarms than in a wired system.

 

Refer to the Serial Interface Users Guide that you can download.

See pages 38 - 41.

Issue an IDENTIFY $01 to the unit (so, a CAL command 2101). The full command would look something like:

\06xxyyzz2101

Where xx = your gateway unit address, yy= the network route (probably 00 as things wont go more than through a single gateway), and zz = the address of the unit on the other side.

You should get an answer back, which is a REPLY containing the unit type.

BEWARE:

1. The reply may take a while to come back - you should set a timeout on the expected reply of about 5 to 10 seconds. More is better.

2. Wireless networks have a higher level of packet loss than wired, you should expected failures.

3. You should not flag a unit as dead or missing until you see about 5 failures in a row.

4. NEVER POLL A UNIT MORE FREQUENTLY THAN ONCE PER 30 MINUTES IN WIRELESS. (This means that if a unit fails you will have a detection time of about 2.5 hours because of the need to detect 5 failures, and you can only do a check every 30 minutes.).

Bear in mind the scaling - if you check a single unit every 30 minutes and have 30 wireless units, thats a check of a unit every 1 minute which is NOT MAKING FRIENDS. You really should be limiting the TOTAL interrogation rate to no more than 1 per 10 minutes.

Also bear in mind that wireless communication to a non-present unit causes a large number of retries (about a dozen); during this period the on-air bandwidth utilisation goes VERY high, and other wireless communication WILL be compromised. Normally this kind of thing only happens during commissioning, and its no big deal. If you are going to have it running all the time you must limit the number and rate of interrogations or you will have some unpleasant consequences.

If all this does not work very well... you were warned!