Protocol is the language. The distance depends not upon the language but the PHYSICAL layer. Is it RS232, RS485 or Ethernet? Each has its own limitations. With good cable, grounding and shields, you can likely get 60 meters with both RS232 and RS485.
Cable quality has a great impact on distance.
There were 2 Modicon processors referenced as "micro". One was the Telemecanique TSX 37 Micro and the other was a "shoebox style" Modicon Micro (3xx,5xx,6xx?). For the Modicon Micro protocol is likely Modbus RS232 serial, for the TSX 37 it is likely Unitelway which is a RS485 type of signal.
Unitelway, with good cables and termination is good for 1000 meters.
RS232, with poor quality cable may max out under 30 meters.
For long runs of RS485, a termination resistor may be necessary. Go to B&B Electronics and review their excellent documentation on serial networks.
If you move them back closer together and they work, then use a 60 meter length of cable at that location (roll it up) and check the comms without having to run back and forth. A basic question, but often true, if a connector was removed to pull the cable, was it properly re-installed?
