Input Connection Scheme - Keithley 7021 Instruction Manual

Card Connections and Installation
7021
Internal connections:
Internal voltage source (+5V) used.
Figure 4-18
Digital output, logic device control

Input connection scheme

Figure 4-19 shows a digital input connection scheme to mon-
itor the state of micro-switches. With a switch open and the in-
put resistor configured for pull up, as shown in Figure 4-19A,
the corresponding input channel is pulled high by the internal
input resistor. As a result, the input channel is high (appears as
a bar on the Model 7001 display or a lit LED on the Model
7002). When a switch is closed, the corresponding input chan-
nel is pulled low to ground. As a result, the input channel is
low (appears as a single dot on the Model 7001 display or an
unlit LED on the Model 7002).
With a switch open and the input resistance configuration set
to pull down, as shown in Figure 4-19B, the corresponding
input channel is pulled low by the internal input resistor. As
a result, the input channel is low. When a switch is closed, the
corresponding input channel is pulled high. As a result, the
input channel is high.
For more information on configuring pull-up resistance, re-
fer to the Configuring digital I/O input pull-up resistance
paragraph.
4-16
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+5V
OUT 31
OUT 32
OUT 33
GND
Logic Device
A
74LS138
DMUX
B
C
V CC
GND
G2A
7021
IN 1
IN 2
IN 3
GND
A. Input resistor is set to pull up.
7021
IN 1
IN 2
IN 3
B. Input resistor is set to pull down.
Y0
Y1
Y2
Y3
Y4
Y5
Y6
Y7
Micro-
switches
Micro-
switches
+V