10.2.1.3 Bus Loading

The RS-485 standard specifies that a compliant driver must be able to drive 32 unit loads (UL), where 1 unit load represents a receiver input current of 1 mA at 12 V, or a load impedance of approximately 12 kΩ. Because the SN65HVD72 and SN65HVD75 have a receiver input current of 150 µA at 12 V, they are 3/20 UL transceivers, and no more than 213 transceivers should be connected to the bus. Similarly, the SN65HVD78 has a receiver input current of 333 µA at 12 V and is a 1/3 UL transceiver, meaning no more than 96 transceivers should be connected to the bus.