Now you've got my attention
Oh, you meant a Siemens/TI 505-series controller, like a 545, not an Allen-Bradley SLC-5/05 controller ! Thank you for that clarification.
So your DeviceNet Scanner is probably a
CTI model 2576.
What's the mix of I/O modules in the FLEX assemblies, discrete vs. analog ? Any unusual modules like the 1203-SM1 SCANPort, or a Modbus module, or a flow computer or high-speed counters ? Is this a high-speed discrete machine control, or a slower continuous process ?
What type of TI-505 CPU are you using ? Do you have any communication modules that can communicate with the ControlLogix, like the CTI 2572-B ?
If you have a 2572-B, you might be able to read the Input and Output data tables of the CTI DeviceNet scanner over EtherNet/IP and use those to run your ControlLogix. You could write logic to not only process the Inputs, but also compare your ControlLogix outputs to the CTI's outputs. You wouldn't have to touch the actual adapters until migration, or install any DeviceNet hardware on the ControlLogix side.
A slightly more involved process might be to install a DeviceNet Scanner on the ControlLogix side (1756-DNB, or 1788-EN2DN) and run Listen Only connections.