If Xpress loses connection to a PLC, after x number of attempts, it will stop and users will have to cycle power to re-connect to the PLC.
Users can turn on Auto-Demotion which is not enabled by default for any channel that will monitor the connection to the PLC and restart the connection.
Here's details from Xpress online help:
Device Properties - Auto-Demotion
Device auto-demotion parameters allow a driver to temporarily place a device off-scan in the event that a device is not responding. By placing a non-responsive device off-line, the driver can continue to optimize its communications with other devices on the same channel by stopping communications with the non-responsive device for a specific time period. After the specific time period has been reached, the driver will re-attempt to communicate with the non-responsive device. If the device is responsive, the device will be placed on-scan, otherwise it will restart its off-scan time period.
Auto-demotion can be enabled by checking the Enable auto device demotion on communication failures as shown below.
The Demote after parameter indicates how many successive cycles of request timeouts and retries will occur before placing the device off-scan. The valid range is 1 to 30 successive failures. The default is 3 successive failures.
The Demote for parameter indicates how long the device should be placed off-scan when the "Demote after" parameter has been reached. During this period no read requests will be sent to the device and all data associated with these read requests will be set to bad quality. The valid range is 100 to 3600000 milliseconds. The default is 10000 milliseconds. When this period expires, the driver will place the device on-scan allowing for another attempt at communications.
The Discard write requests during the demotion period parameter allows you to control whether or not write requests should be attempted during the off-scan period. The default setting is to always send write requests regardless of the demotion period. If you choose to discard writes, the server will automatically fail any write request received from a client and will not post an "Unable to write..." messages to the server event log.
To determine when a device is off-scan by monitoring its demoted state, use the _AutoDemoted System Tag for this device.