When Send Outputs on Startup is enabled for Series 2 redundant Serial cards, the lastoutput value is sent to the Modbus devices connected to the serial port when the cards switchover. If the values in your Modbus devices change frequently, it is recommended that you enable Output Readback on the output datasets to ensure that the Modbus devices maintain their values. Refer to the following topic, Using Outputs in Control Modules, for more information on this option.