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Chapter 2 Hardware Overview
© National Instruments Corporation 2-3 NI PCI-8254R User Manual
Table 2-1 summarizes the TTL inputs and outputs available on the
NI 8254R.
Isolated Inputs and Outputs
The isolated inputs and outputs on the NI 8254R have a separate ground
reference from the main NI 8254R supply, providing an easy means to
prevent ground loops that can introduce noise into a system. You can apply
signals up to 30 V to the isolated inputs. The voltage swing of the isolated
outputs is determined by the voltage you supply on the 2-position isolated
outputs power connector.
Note V
iso
is referred to as V, and C
iso
is referred to as C on the 2-position isolated outputs
power connector on the NI 8254R.
Note The isolated outputs have current-limiting protection circuitry. If this circuitry is
tripped, you can re-enable the outputs by removing the fault and restarting your computer.
Table 2-1. NI 8254R TTL Inputs and Outputs
Primary
Function
Input
or
Output
Number
Available
Signal Names
44-Pin
D-SUB on
NI 8254R
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, Pulse4
TRIG 1, Pulse 5
TRIG 2, Pulse 6
4
6
7
18
24
9
5
7
8
20
—
—
Watchdog Output 1 TTL Output 0 3 4
General
Purpose
Output 3 TTL Output 5
TTL Output 6
TTL Output 7
19
21
22
21
23
24
* TTL Input 0 and TTL Input 1 can also function as trigger change detectors.