User`s manual

MGate 4101-MB-PBS UM Quick Configuration
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Sync & Freeze are optional slave services and may not be supported by some slaves. A master uses a Freeze
telegram to make a slave or group of slaves freeze their inputs in the current state. A Sync telegram causes the
output data currently available to be transferred to the outputs, to be frozen. An Unsync & Unfreeze command
will cancel this state. The Clear Data service allows the outputs to be switched to a defined state if an error
occurs. The response parameter Status can be tested to indicate whether transmission of the request frame
was successful or not, with possible values of: OK, DS, NO, and IV.
Use of Freeze
In closed-loop control systems and for the synchronization of drives, etc., it is sometimes necessary to have a
precise time image of the process inputs of a group. Freeze is used to accomplish this as follows:
The master sends a Freeze command to the selected group (A global control telegram goes to the selected
group at a precise time). This causes all addressed slaves to freeze their inputs. During the next Data
Exchange cycle, the slaves transfer the frozen inputs of the group to the master.
After the master receives this data, the master sends an Unfreeze command to the group and the bus system
returns to the normal data exchange mode again, and all input changes are transferred during each data cycle.
Use of Sync/Unsync
For the time-controlled operation of output devices which belong to a group, sync and unsync are used as
follows:
After the data is frozen with a Freeze command and has been processed by the master, the master reacts by
sending a sync command to the slave group to obtain the outputs. During the next data cycle, the master
supplies the slave group with the data to be output, then concludes this cycle with an unsync command in the
following data exchange cycle. Unsync causes the slaves to transfer their outputs at a precise time.
Support Function
MGate 4101-MB-PBS supports the global control functions mentioned above, such as freeze/unfreeze,
sync/unsync and clear data. Thanks to these functions, the MGate 4101-MB-PBS can be adopted by more
applications and is more powerful.l
Modbus Overview
Introduction
Modbus is one of the most popular automation protocols in the world. It supports both serial and Ethernet
devices. Many industrial devices, such as PLCs, DCSs, HMIs, instruments, meters, motors, and drivers, use
Modbus as their communication standard.
Devices are Either Masters or Slaves
All Modbus devices are classified as either a master or a slave. Masters initiate all communication with slaves
and do not communicate to other masters. Slaves are completely passive and communicate only by sending a
response to a master’s request.