| Author |
Message |
prasi
Guest
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 Posted:
Wed Nov 30, 2005 9:15 am Post subject:
which device will be slave/client and which one will be mast |
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hi
I Have one basic doubt,I was reffering the specification of MODBUS TCP,
I got confused.
According to my understanding, the controlling device i.e the RTU(Real
Time Unit) will be the slave and the one who request(poll) for the data
is the master.
But in case of client/server concept the one who serves the
request(RTU) will be the server and one poll for the data is the
client.
Please clarify my doubt
Thanks in advance
Prasi |
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Grant Edwards
Guest
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| Posted:
Wed Nov 30, 2005 5:15 pm Post subject:
Re: which device will be slave/client and which one will be |
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On 2005-11-30, prasi <kp.prasanna@gmail.com> wrote:
| Quote: | I Have one basic doubt,I was reffering the specification of
MODBUS TCP, I got confused. According to my understanding, the
controlling device i.e the RTU(Real Time Unit)
|
RTU stands for "remote terminal unit". It's generally a slave
device that provides I/O points for use by the master.
| Quote: | will be the slave and the one who request(poll) for the data
is the master.
|
Correct.
| Quote: | But in case of client/server concept the one who serves the
request(RTU) will be the server and one poll for the data is
the client.
|
Exactly.
The RTU (the remote I/O device) is the slave. In TCP terms,
it's probably the server. The control system that reads/writes
data to/from the RTU is the master (the client in TCP terms).
--
Grant Edwards grante Yow! I KAISER ROLL?! What
at good is a Kaiser Roll
visi.com without a little COLE SLAW
on the SIDE? |
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Grant Edwards
Guest
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| Posted:
Wed Nov 30, 2005 5:15 pm Post subject:
Re: which device will be slave/client and which one will be |
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On 2005-11-30, Thad Smith <ThadSmith@acm.org> wrote:
| Quote: | prasi wrote:
hi
I Have one basic doubt,I was reffering the specification of MODBUS TCP,
I got confused.
According to my understanding, the controlling device i.e the RTU(Real
Time Unit) will be the slave and the one who request(poll) for the data
is the master.
That sounds correct.
But in case of client/server concept the one who serves the
request(RTU) will be the server and one poll for the data is
the client.
The master/slave allocation is a low-level communication synchronization
concept. It says nothing about which end requests data. You may have
one master and several slave units.
Either master or slave may make a request of the other unit,
|
That's not true in older Modbus (non TCP) systems.
Traditionally, Modbus is a single master bus. Only the master
my make a request.
Is Modbus TCP multi-master, or has the master-slave thing been
thrown out completely, and it's all peer-to-peer where any device
can send a request to any other device? In that case, all
devices are both clients and servers in TCP terminology.
| Quote: | depending on how the system is designed. The client/server
model is better suited for independently running clients. A
realtime system is usually more coordinated and doesn't fit
the client/server model as well, especially with cental
control.
|
--
Grant Edwards grante Yow! ... I have read the
at INSTRUCTIONS...
visi.com |
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Thad Smith
Guest
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| Posted:
Wed Nov 30, 2005 5:15 pm Post subject:
Re: which device will be slave/client and which one will be |
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|
prasi wrote:
| Quote: | hi
I Have one basic doubt,I was reffering the specification of MODBUS TCP,
I got confused.
According to my understanding, the controlling device i.e the RTU(Real
Time Unit) will be the slave and the one who request(poll) for the data
is the master.
|
That sounds correct.
| Quote: | But in case of client/server concept the one who serves the
request(RTU) will be the server and one poll for the data is the
client.
|
The master/slave allocation is a low-level communication synchronization
concept. It says nothing about which end requests data. You may have
one master and several slave units.
Either master or slave may make a request of the other unit, depending
on how the system is designed. The client/server model is better suited
for independently running clients. A realtime system is usually more
coordinated and doesn't fit the client/server model as well, especially
with cental control.
--
Thad |
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