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101
Operating the Network
Section 3-6
groups at the same time, or to no specific group at all. The group assignment
is sent to the slave devices as part of the parameter message.
To define the group assignment of a slave device, through the Generic Slave
DTM, refer to section
3-3-3 Selecting the Group Assignment
.
Freeze / Unfreeze
commands
Sending a Global-Control - Freeze command to a slave device has the follow-
ing effect
• The slave device will continue to read its physical inputs, but not send this
data to the PROFIBUS Master Unit.
• Instead, it will continue to transfer the input data to the Master Unit from
the moment the Global-Control - Freeze command was received.
• If a new Global-Control - Freeze command is sent, the slave device will
update its PROFIBUS input buffers only once, with the most recent physi-
cal input data, and continue to transfer this data to the Master Unit with
subsequent I/O data exchange messages.
• If a Global-Control - Unfreeze command is sent, the slave device will
revert back to its original situation, and transfer updated input information
to the Master Unit with subsequent I/O data exchange messages.
Note
If a Global-Control command contains both a Freeze and an Unfreeze com-
mand, the Unfreeze will prevail.
The figure shown below illustrates the Freeze / Unfreeze feature as imple-
mented by the CS1/CJ1W-PRM21 PROFIBUS Master Unit.
Note
The Global-Control command as set in the CIO words is transferred to the
Unit together with the I/O data, but the Global-Control command is sent over
the PROFIBUS network, following the I/O data. The Freeze command forces
an immediate update of the PROFIBUS transmission buffers in the slave
device, with the last input value sampled. This input data is then transferred to
the PROFIBUS Master Unit, with the next I/O data exchange cycle.
PLC Cycle
PROFIBUS
Cycle
Global-Control Freeze command
Global-Control Freeze command
Freeze
transmitted
Instruction
Execution
Instruction
Execution
Instruction
Execution
Instruction
Execution
Freeze command freezes
slave input refresh process.
Last input data transferred to
transmit buffer will be
transferred over PROFIBUS.
Global-Control Unfreeze command
Unfreeze
transmitted
Unfreeze command cancels
Freeze command and causes
immediate update of transmit
buffer. Input refresh process
started again.
Slave
PROFIBUS
Input Buffers
Slave Input
Refresh Cycle
Freeze
transmitted
Freeze command causes
immediate update of transmit
buffer. Last sampled data will be
transferred over PROFIBUS.