In an RS-485 network, the distance between the transceiver inputs and the cable trunk is known as the stub. The stub should be as short as possible when a node is connected to the bus. Stubs are a non-terminated piece of bus line that can introduce reflections of varying phase as the length of the stub increases. The electrical length, or round-trip delay, of a stub should be less than one-tenth of the rise time of the driver as a general guideline. Therefore, the maximum physical stub length (L(STUB)) is calculated as shown in Equation 3.

where:

• tr is the 10/90 rise time of the driver.
• c is the speed of light (3 × 108 m/s).
• v is the signal velocity of the cable or trace as a factor of c.