User`s manual

Configuring the Agilent E1330B Digital I/O Module 19
Chapter 2
Enabling Pull-ups
Referring to Figure 2-1, note the pull-up enable jumpers near the middle of
each of the large ICs. The data lines of each port can be independently
configured for either passive or active pull-up to TTL high levels. The
factory-shipped condition is pull-up disabled for all ports. The data lines
may be either inputs or outputs. When the data lines are outputs, and the
jumper is in the enabled position, the outputs are actively forced high. When
the data lines are inputs, the jumper position makes no difference.
Note The jumper in the enabled position does not add an input pull-up resistor to
each data line, it enables a chip-internal pull-up network.
Each data line has an active resistive terminating network. The active
circuitry ensures that when power is removed from the module, the data
lines are not loaded. With power applied, the resistive terminating network
is equivalent to that shown in Figure 2-3.
Figure 2-3. Equivalent Data Line Termination