There is an inverse relationship between data rate and bus length, meaning the higher the data rate, the shorter the cable length; and conversely, the lower the data rate, the longer the cable can be without introducing data errors. While most RS-485 systems use data rates between 10 kbps and 100 kbps, some applications require data rates up to 250 kbps at distances of 4000 feet and longer. Longer distances are possible by allowing for small signal jitter of up to 5 or 10%.

Figure 9-3 Cable Length vs Data Rate Characteristic

Even higher data rates are achievable (such as 26 Mbps for the SN65HVD30 and SN65HVD33 devices) in cases where the interconnect is short enough (or has suitably low attenuation at signal frequencies) to not degrade the data.