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From: markp on 21 Jul 2010 10:05
Hi All,

I'm designing a Profibus interface. I'm a little confused with the +5V
termination power supply (Voltage Plus, or VP). My understanding is that VP
is supplied by something on a segment that is used to actively terminate all
the receivers, and usually these resistors are in the Profibus connectors
themselves.

So:
Is it the master only that drives VP onto the bus?

If my device can be a master or slave, I presume I have to be able to either
drive VP or not depending on whether I'm a master or not (?)

What is the current requirement of VP?

Also, for bog standard RS485 applications I usually use isolated 5V supplies
locally on each receiver, and a common signal ground reference linking them.
Is that usual with Profibus too?

I guess the master would generate VP referenced to this same common ground
signal, I assume using an isolated supply. Which means if I already have an
isolated supply as part of the reciever section I could use that directly to
drive VP (?)

Sorry for all the questions, I can't seem to find any docs that tie this
down.

Mark


From: JosephKK on 25 Jul 2010 15:30
On Wed, 21 Jul 2010 15:05:48 +0100, "markp" <map.nospam(a)f2s.com>
wrote:

>Hi All,
>
>I'm designing a Profibus interface. I'm a little confused with the +5V
>termination power supply (Voltage Plus, or VP). My understanding is that VP
>is supplied by something on a segment that is used to actively terminate all
>the receivers, and usually these resistors are in the Profibus connectors
>themselves.
>
>So:
>Is it the master only that drives VP onto the bus?
>
>If my device can be a master or slave, I presume I have to be able to either
>drive VP or not depending on whether I'm a master or not (?)
>
>What is the current requirement of VP?
>
>Also, for bog standard RS485 applications I usually use isolated 5V supplies
>locally on each receiver, and a common signal ground reference linking them.
>Is that usual with Profibus too?
>
>I guess the master would generate VP referenced to this same common ground
>signal, I assume using an isolated supply. Which means if I already have an
>isolated supply as part of the reciever section I could use that directly to
>drive VP (?)
>
>Sorry for all the questions, I can't seem to find any docs that tie this
>down.
>
>Mark
>

Try this, i think it looks promising:

http://www.profibus.com/nc/downloads/downloads/profibus-technology-and-application-system-description/display/
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