National Instruments 6024E Benutzerhandbuch
Chapter 4
Signal Connections
4-24
ni.com
Power-up State
♦ 6025E only
The 6025E contains bias resistors that control the state of the digital I/O
lines PA<0..7>,PB<0..7>,PC<0..7> at power up. Each digital I/O line is
configured as an input, pulled high by a 100 k
lines PA<0..7>,PB<0..7>,PC<0..7> at power up. Each digital I/O line is
configured as an input, pulled high by a 100 k
Ω bias resistor.
You can change individual lines from pulled up to pulled down by adding
your own external resistors. This section describes the procedure.
your own external resistors. This section describes the procedure.
Changing DIO Power-up State to Pulled Low
Each DIO line is pulled to V
cc
(approximately +5 VDC) with a 100 k
Ω
resistor. To pull a specific line low, connect between that line and ground
a pull-down resistor (R
a pull-down resistor (R
L
) whose value gives you a maximum of 0.4 VDC.
The DIO lines provide a maximum of 2.5 mA at 3.7 V in the high state.
Using the largest possible resistor ensures that you do not use more current
than necessary to perform the pull-down task.
Using the largest possible resistor ensures that you do not use more current
than necessary to perform the pull-down task.
However, make sure the value of the resistor is not so large that leakage
current from the DIO line along with the current from the 100 k
current from the DIO line along with the current from the 100 k
Ω pull-up
resistor drives the voltage at the resistor above a TTL-low level of 0.4 VDC.
Figure 4-12 shows the DIO configuration for high DIO power-up state.
Figure 4-12 shows the DIO configuration for high DIO power-up state.
Figure 4-12. DIO Channel Configured for High DIO Power-up State with External Load
Example
A given DIO line is pulled high at power up. To pull it low on power up with
an external resistor, follow these steps:
an external resistor, follow these steps:
1.
Install a load (R
L
). Remember that the smaller the resistance, the
greater the current consumption and the lower the voltage.
Device
Digital I/O Line
82C55
100 k
GND
R
L
+5 V