YASKAWA VIPA System 300S Manual page 25

Manual VIPA System 300S
Master and slaves
Master class 1
MSAC_C1
Master class 2
MSAC_C2
HB140E - IM - RE_353-1DP01 - Rev. 14/47
PROFIBUS distinguishes between active stations (master) and passive
stations (slave).
Master devices
Master devices control the data traffic at the bus. It is also possible to
operate with multiple masters on a PROFIBUS. This is referred to as multi-
master operation. The protocol on the bus establishes a logical token ring
between intelligent devices connected to the bus. Only the master that has
the token, can communicate with its slaves.
A master is able to issue unsolicited messages if it is in possession of the
access key (token). The PROFIBUS protocol also refers to masters as
active participants.
Slave devices
A PROFIBUS slave acquires data from peripheral equipment, sensors,
actuators and transducers. The VIPA PROFIBUS couplers are modular
slave devices that transfer data between the System 300V periphery and
the high-level master.
In accordance with the PROFIBUS standards these devices have no
bus-access rights. They are only allowed to acknowledge messages or
return messages to a master when this has issued a request. Slaves are
also referred to as passive participants.
The master of the class 1 is a central control that exchanges cyclically
information with the decentral stations (slaves) in a defined message cycle.
Typical MSAC_C1 devices are controls (PLC) or PCs. MSAC_C1 devices
gain active bus access which allows them to read the measuring values
(inputs) of the field devices and to write the set points (outputs) of the
actuators at a fixed time.
MSAC_C2 are employed for service and diagnostic. Here connected
devices may be configured, measuring values and parameters are
evaluated and device states can be requested. MSAC_C2 devices don't
need to be connected to the bus system permanently. These also have
active bus access.
Typical MSAC_C2 devices are engineering, project engineering or operator
devices.
Chapter 3 Deployment
3-3