Keithley 7037, Instruction Manual

Page: 31 / 72

Card Connections and Installation
4-12
Logic device control —
Figure 4-14 shows a digital output
connection scheme to control a logic device. This example
assumes that an in5V voltage source is being used.
Figure 4-14
Digital output, logic device control
The logic device is a demultiplexer (DMUX). The binary
pattern (value) seen at the input of the DMUX (lines A, B,
and C) determines which DMUX output line (Y0 through
Y7) is selected (pulled low). For example, with channels 1,
2, and 3 off (open), lines A, B and C are high. The binary 7
at the DMUX input (A = 1, B = 1 and C = 1) selects (pulls
low) output Y7. If channel 32 is turned on (closed), line B
goes low. The binary 5 seen at the DMUX input (1, 0, 1)
selects (pulls low) Y5.
Input connection scheme
Figure 4-15 shows a digital input connection scheme to mon-
itor the state of micro-switches. With a switch open and the
input resistor conf gured for pull up as shown in
Figure 4-15a, 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 corre-
sponding input channel 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).
Figure 4-15
Digital input, monitoring micro-switches
With a switch open and the input resistance conf guration set
to pull down as shown in Figure 4-15b, 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 conf guring pull-up resistance,
refer to the Conf guring digital I/O input pull-up resistance
paragraph.
OUT 31
7037
OUT 32
Internal connections:
Internal voltage source (+5V) used.
OUT 33
+5V
GND
Y0
Y1
Y2
Y3
Y4
Y5
Y6
Y7
Logic device
74LS138
DMUX
V
CC
GND
A
B
C
G2A
IN 2
IN 1
Micro-
switches
7037
IN 3
GND
A. Input resistor is set to pull up.
IN 2
IN 1
Micro-
switches
7037
IN 3
B. Input resistor is set to pull down.
+V