There are programmable logic controllers in our catalog where you can connect to a computer using a special connector specifically made for the unit. Sometimes, certain units tend to hide the access ports behind panels that aren’t immediately obvious. One specific product that has been asked about before is manufacturer part number 88970051; Digi-Key part number 646-1100-ND where the port could not be found. It turns out there is a panel on the front next to the screen on the right that looks like a rectangle, this actually can be pried off on the right side of the panel where the indent is. I was able to find documentation showing this: http://media.crouzet.com/catalog/_inst-sheets/AU_LC_M3_Installation-Sheets_NTR772-01A55_ML.pdf using Crouzet’s product search. The installation sheet is located here: 88970051 Microcontroleur 3 M3 Essential Cd20-24Vdc....
It turns out this is a common design for many Crouzet PLCs, here is a list of all Crouzet PLCs we have in stock: https://www.digikey.com/short/m7tpjpdz. Many of them have that similar-looking rectangle panel or what may be panels with no labels showing where access might be. I would advise checking what datasheets we have listed for these products first. If the info isn’t there, there may be similar documentation on Crouzet’s website compared to 88970051 by searching for the product number on Crouzet’s website and looking for an installation guide.
It also seems like this is a common practice by many PLC manufacturers besides Crouzet (see complete stocking list here). I would assume these panel designs are used to protect the sensitive ports. It’s not always obvious that the panels are “removable” or point to what they are hiding. I would also suggest reading the datasheets available if you can’t find the access ports first. I would then check the manufacturer’s website with their part numbers to see if there is better documentation. If you are unsuccessful, you can always ask us here on the Forum.