Unit Status Tab

ok,

Toolkit V1.5.0

I was on site the other day chasing a strange problem of a Dimmer not responding occasionally when I noticed something else.

In toolkit if you go into the GUI of a Dimmer or relay unit, On the status tab with units on the network, the 'Clock Gen' (or something like that ) LED was not lit up on the units that had the 'Enable C-Bus Clock' check box ticked.
Has anyone else noticed this and if so is it a defect?

 

Yep, thats sounds right thinking it about it now.

I made sure there were only three units with the check box ticked. However I thought I checked all three units and none of them had the LED in the status tab lit up. Might have been wrong though .

 

C-Bus comms is based on 802.1 using CSMA/CD/CA. Comms is not possible without a clock pulse present on the bus. The clock pulse enables all units to time aspects of their comms.

$1.00 prize to the first person who can give the full descroption for CSMA/CD/CA as applied to the C-Bus protocol.

 

And I will give you $1.00 if you can spell DESCRIPTION correctly...

 

OK smarty, I touch type - some days better than others. The truth is I tend to get a bit lazy when typing because most apps pick up bad spelling/typing and it is quicker to use this, than drop your fingers off the home keys on the keyboard, to get to the arrow back or grab the mouse.

Now you have stuck your head out of your kennel what does CSMA/CD/CA stand for.

And yes the $1.00 offer stands for people in the dear friends category, which I include you in

PS if I don't see the red line under a word I don't waste time reading my own typing because I know what I meant and that's all that matters.

 

C-Bus protocol is not based on 802.1., though it may share some similarities. Most Carrier Sense Multiple Access protocols with Collision Detection (CSMA/CD) have similar frame construction, with headers, identifiers, data payload, checksum and timeslots for acknowledgement of correctly received frames. That's about all.

The way Wired C-Bus works in this regard is quite simple: A Data '1' bit drives the bus with a predefined bipolar pulse of about 2.5V amplitude and a source impedance on the order of 10 Ohms. A data '0' is a period of the same duration as a data '1', but the bus is left open-circuit. With C-Bus, the data bit timings are sufficiently long so that with a bus length of up to 1km, any transients due to reflections from mismatched terminations will die out well before the receiver sampling time for each bit, so C-Bus can use a BIT-WISE Collision detection..This allows lossless Collision Avoidance (the CA part) with NO time penalty (transmitters which did not achieve bus control due to a collision can retry without any need for a holdoff period, as soon as the bus is free again, and collisions do not cause any corruption of data for the winning transmitter frame)

The clock waveform is used to synchronise the start timing of all data bits, so that this collision avoidance can be achieved without the need for a "preamble". If C-Bus did not use a clock, it could still work in much the same way, but it would need some sort of preamble, which would have to be on the order of one bit-time or more to ensure that it was effective. The clock is just as easy to implement, and it also provides a network-wide timing reference for all sorts of things for free!

Do I get the $1.00?

 

One shiny dollar please...

CSMA/CD/CA

Carrier Sense Multiple Access / Collision Detection / Collision Avoidance.

Straight out of the Black Box pocket glossary of computer terms book!

Mark

 

Don,

That's not fair, you didn't give anyone a chance.

I will dig out some old C-Bus training / specification litrature that states C-Bus is based on 802.1. (actually looking across my office I can see the folder in my bookcase)

When I get a moment I will read and digest your post as it is comprehensive. From what you have writte the clock pulse is a fundamental aspect of the C-Bus comms as it stands though.

PM me with an address and I will send a money order for $1.00

 

Mr Mark

Looks like Don beat you to it, unless you wish to lodge a protest regarding his long term involvement with C-Bus development - his post is a good one though and well worth the dollar spent.

 

Must learn to type faster, or use more than two fingers!
I concede defeat.... Mr Don wins (again!)