KB013 How long could be the RS-422 / RS-485 or SSI signal cable?

RS-422 / RS-485 and SSI are differential serial data interfaces designed for long data cables. The cable length depends on the cable quality and data rates.
See the following guidelines for the RS-422 / RS-485 interfaces:

  • 19’200 Baud → up to 1000m
  • 115’200 Baud → up to 500m

See the following guidelines for SSI interfaces:

  • ≤ 100kBit/s → up to 1000m
  • ≤ 500kBit/s → up to 200m
  • ≤ 1000kBit/s → up to 100m

Cable type and termination:

  • Use shielded twisted pair cables only
  • Termination according to characteristic impedance of the cable (typ. 100 … 150 Ω)

The cable length is also influenced positively / negatively by other factors:

  • Quality of the cable (Shielding, cross-section, wire resistance, etc.)
  • Environmental conditions (Disturbance sources like motors, etc.)

Further details in the Technical Reference Manual (see Downloads).