Specifications

Chapter 2 - System Configuration RS-422 And RS-485 Applications Ebook
Page 37 of 137 Manual Documentation Number: <DocNumber>
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Current through the voltage divider is approximately 2.23 mA. The
voltage across the signal lines (V
AB
) is -2.7 V. This is much more than
the target -300 mV, which ensures good idle state biasing.
Figure 25: 10 Node RS-485 Network with no termination resistors
Notice that without termination resistors the current requirements are
significantly less than when termination resistors are used. In this case
adding nodes with built-in biasing resistors does not change the idle
state voltage significantly (because the voltage divider scales
proportionately), but it does increase the current. Decreasing nodes
also does not change the voltage significantly, but does decrease the
amount of current required. Ultimately, the example shows that the
standard 4.7 k biasing resistors are an appropriate value for most