Chapter 2
Digital I/O
2-2
ni.com
NI-IMAQ I/O devices such as the such as the NI 8254R, the NI 8255R, and
the CVS-1450 Series Compact Vision Systems have 29 digital I/O lines
with built-in functionality for communicating with external devices, such
as reading quadrature encoder inputs, generating strobe pulses, and writing
to or reading from digital lines.
NI-IMAQ I/O devices have 15 digital input lines—13 isolated 24 V lines
and two dedicated TTL lines. There are 14 digital output lines—four
isolated 24 V lines and 10 dedicated TTL lines. Using these signals, you
can dynamically control your lighting or cameras, synchronize with a
conveyor belt, or communicate with relays that control solenoids and other
actuators.
TTL Inputs and Outputs
TTL is a fast-switching 5 V digital signaling standard commonly used for
applications that require high precision, such as camera triggering. TTL
inputs and outputs do not require a separate power supply.
Caution
Do not connect voltage or current sources to TTL outputs. Doing so could
damage the NI 8254R device.
Table 2-1 summarizes the TTL inputs and outputs available on the
NI 8254R.
Table 2-1. NI 8254R TTL Inputs and Outputs
Primary
Function
Input
or
Output
Number
Available
Signal Names
44-Pin
D-SUB on
NI 8255R
Device Pin
Number
37-Pin
Terminal
Block
Number
Trigger
Input
2
TTL Input 0,
General Purpose
*
TTL Input 1,
General Purpose
*
1
16
1
2
Timed
Pulse
Output
6
TTL Output 1, Pulse 1
TTL Output 2, Pulse 2
TTL Output 3, Pulse 3
TTL Output 4, Pulse
TRIG 1, Pulse 5
TRIG 2, Pulse 6
4
6
7
18
24
9
5
7
8
20
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