Newbie question: Concurrent transmission

[tinska.h]

Greetings,

Can someone point out what are the methods to transmit simultaneously/asynchronously between many slaves or nodes to the host, by using only one conductor?

For example, in I2C, master uses address to select which slave can transmit data. Or SPI uses CS to select which slave to communicate. How can one transfer data without addressing or chip selects? Howabout in Power Line Communications, assumingly there are multiple nodes that want to transmit data to another, how can each node determine when to transmit the data without packet collisions? Or is it always controlled by a host?

Is there ANY methods to transmit data over single conductor (+ground of course) without the need of host telling the clients/slaves when to transmit, or who is able to transmit?


I'm very new in the communications area, so any advice or pointers are more than welcome.

Thanks in advance!


- Tinska

 

[KlausST]

Hi,

without packet collisions?

I think this is the key. Either you have timed slots for each slave to transmit data to the host (like USB),
or the slaves transmit randomly. For sure they need to listen to the dataline and wait until a still running communication ends.
But then it tries to get access to the bus. Either with a true arbitration process or just by sending.
With both methods you get collisions. But you have to detect these collisions and if it happens the slave has to wait and retry.

Usually all these methodes include a dedicated protocol and redundancy check to avoid wrong data.

Klaus

 

[kripacharya]

Without some form of arbitration you have to deal with a system which includes collision detection & recovery. There are many schemes for doing this. Look for CSMA/ CD

With arbitration I do not see why there would be collisions ? @KlausST ?

 

[KlausST]

Hi,

With arbitration I do not see why there would be collisions ? @KlausST ?

collisions may occur during the start of arbitration phase.
When two or more slaves try to get the bus at the same time.
After arbitration there should be no collisions.


Klaus