National Instruments NI 6120 - Manual (Page 45)

Chapter 4 Connecting Signals
© National Instruments Corporation 4-7 NI 6115/6120 User Manual
Types of Signal Sources
When making signal connections, you must first determine whether the
signal sources are floating or ground-referenced. The following sections
describe these two types of signals.
Floating Signal Sources
A floating signal source is not connected in any way to the building ground
system but, rather, has an isolated ground-reference point. Some examples
of floating signal sources are outputs of transformers, thermocouples,
battery-powered devices, optical isolator outputs, and isolation amplifiers.
An instrument or device that has an isolated output is a floating signal
PFI3/GPCTR1_SOURCE DIO — V
CC
+0.5 3.5 at
(V
CC
–0.4)
5 at 0.4 1.5 50 k Ω
pu
PFI4/GPCTR1_GATE DIO — V
CC
+0.5 3.5 at
(V
CC
–0.4)
5 at 0.4 1.5 50 k Ω
pu
GPCTR1_OUT DO — — 3.5 at
(V
CC
–0.4)
5 at 0.4 1.5 50 k Ω
pu
PFI5/UPDATE* DIO — V
CC
+0.5 3.5 at
(V
CC
–0.4)
5 at 0.4 1.5 50 k
Ω
pu
PFI6/WFTRIG DIO — V
CC
+0.5 3.5 at
(V
CC
–0.4)
5 at 0.4 1.5 50 k Ω
pu
PFI7/STARTSCAN DIO — V
CC
+0.5 3.5 at
(V
CC
–0.4)
5 at 0.4 1.5 50 k Ω
pu
PFI8/GPCTR0_SOURCE DIO — V
CC
+0.5 3.5 at
(V
CC
–0.4)
5 at 0.4 1.5 50 k Ω
pu
PFI9/GPCTR0_GATE DIO — V
CC
+0.5 3.5 at
(V
CC
–0.4)
5 at 0.4 1.5 50 k Ω
pu
GPCTR0_OUT DIO — V
CC
+0.5 3.5 at
(V
CC
–0.4)
5 at 0.4 1.5 50 k Ω
pu
FREQ_OUT DO — — 3.5 at
(V
CC
–0.4)
5 at 0.4 1.5 50 k Ω
pu
pu = pull up; pd = pull down; DO = Digital Output
The tolerance on the 50 k
Ω pull-up and pull-down resistors is very large. Actual value may range between 17 and 100 kΩ.
Table 4-5. Digital I/O Signal Summary (Continued)
Signal Name
Signal
Type and
Direction
Impedance
Input/
Output
Protection
(Volts)
On/Off
Source
(mA at V)
Sink
(mA at V)
Rise
Time
(ns) Bias