Modbus Unsolicited Serial Driver: tags have good quality before they've been written to by the Modbus client.

Starting with TOP Server version 4.200.353, the Modbus Unsolicited driver has a Device Properties option called "OPC quality bad until write". Prior to that server version, the driver always operated as though this option were off (all tags had good quality from startup). If you turn on the "bad until write" option, tags in the driver will have bad quality until the memory location(s) referenced by the tags have been written to by a Modbus command or client application.

This option can be helpful in scenarios like the following:

Modbus client --> unsolicited driver --> LinkMaster --> link outputs to an OPC server

If "OPC quality bad until write" is turned off, then when the system starts up, LinkMaster will write zeros to the link outputs before the Modbus client has written anything to the Unsolicited driver.

Once "OPC quality bad until write" is turned on, LinkMaster will not write to the link outputs until the Modbus client has written to the unsolicited driver.