The "shoebox" style SLC-500 controllers such as the 1747-L40C have only a Data Highway 485 (DH485) proprietary network connector.
That port on the 1747-L40C looks similar to an Ethernet connector but is NOT the same; do not connect it to an Ethernet cable or device. There is +24V on one of the pins and it will very probably damage any Ethernet device you connect.
The MicroLogix 1400 supports Data Highway 485 protocol through both its Channel 0 (round mini-DIN style with RS-232 and RS-485 wiring) and Channel 1 (Dsub-9 RS-232).
How far apart are the controllers ? If they are only a few meters, you may be able to connect using a custom cable between the non-isolated MicroLogix Channel 0 port with a
1763-NC01 wiring adapter and the 1747-L40C's DH485 jack.
Otherwise you will probably use a 1761-NET-AIC, which is an RS-232 / RS-485 converter and isolator.