Ashcroft DM61 - Manual (Page 14)

Serial Communication Adapters Instruction Manual
14
Figure 2. RS-485 Full-Duplex Four-Wire Wiring
Notes:
1. Termination resistors are optional and values depend on the cable
length and characteristic impedance. Consult the cable manufacturer
for recommendations.
2. Use shielded cable, twisted-pairs plus ground. Connect ground shield
only at one location.