ABB AC 900F Mounting And Installation Instructions Manual page 93

Section 6 Wiring
RS485
RS485 redundant PM.png
A regulated power supply with output voltage 5 V DC +/- 10% is needed to provide
for a defined quiescent level on the RS484 bus. .
The 5 V DC power supply unit must have a safe electrical isolation. As described
earlier in this section, the external resistors must be protected against electrostatic
discharge.
M&I – AC 900F Controller
Serial interfaces of the CPU module
93