M
M Griffin
The AVR board looks like it would do the job for a Modbus/TCP interface, provided it works with the I/O rack (I'm assuming you've already looked into that). The web server would also be useful for configuring the rack and for troubleshooting and commissioning I/O. SSH/SCP and/or FTP could be used to upload new software ("firmware upgrades"). All of those "extra" features are actually quite important to make a system usable.