SN65HVD78: SN65HVD78 rate related issues

That figure was created at a time when RS-485 was not intended go above 10 Mbps; the SN65HVD78 supports more.

But the speed is limited not only by the transceiver but also by the jitter introduced by the cable; a faster transceiver cannot work around a long cable.

With a 60 m cable, you could get 2 Mbps with very low jitter, or 20 Mbps with 5 % jitter. You have to know how much jitter your receivers can tolerate; when in doubt, test it, and stay far away from data rates where you begin to get errors.

Hi Jeno,

Clemens is correct.

The chart is based on classical RS-485 where 10Mbps is the max speed - more modern devices can go faster - but as you push above 10Mbps you will see shorter bus lengths.  With that being said conservatively at 60m you should get about 2Mbps and possibly faster if the receiver/processor  in the system can handle a higher amount of jitter introduced by the cabling + speed.

It is very important to note that this chart assumes an ideal setup system as well - so 22AWG 120 ohm cabling with no stub length violation,  both ends are properly terminated, and the bus is not overloaded. Ideally you should always aim for ideal setups but that's not going to happen in every application.  

Please let me know if you have any other questions and I will see what I can do!

Best,

Parker Dodson