Chapter 7
Biasing the entire network requires one pair of resistors. Networks that use a
primary/secondary protocol typically place the biasing resistors at the primary
node. If a node becomes disconnected from the network or a network wire
opens, the internal fail-safe circuits hold the inputs at logic 1.
The external fail-safe components have a small effect on the current. When a
driver is enabled and line A is more positive than line B, the output current is in
the same direction as the bias current, so the two currents add. When the driver
brings line B more positive than line A, the bias current is in the opposite direc-
tion and subtracts from the signal current. But because the drive current isFigure 7-10: Open-circuit biasing ensures a logic 1 logic state when the line is open
or no driver is active.