National Instruments NI VISION PCI-8254R 用户手册

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Table 2-1 summarizes the TTL inputs and outputs available on the 
NI 8254R.

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.

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.

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

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.