Chapter4 SignalConnections
6023E/6024E/6025EUser Manual 4-24 ni.com
Power-up State
♦6025E only
The 6025E contains bias resistors that control the state of the digital I/O
linesPA<0..7>,PB<0..7>,PC<0..7> at power up. Each digital I/O line is
configuredas an input, pulled hig hby a 100 kΩbias resistor.
Youcan change individual lines from pulled up to pulled down by adding
yourown external resistors. This section describes the procedure.
Changing DIO Power-up State to Pulled Low
EachDIO line is pulled to Vcc (approximately +5 VDC) with a 100 kΩ
resistor. To pull a specific line low, connect between that line and ground
apull -down resistor (RL) 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.
Usingthe largest possible resistor ensures that you do not use more current
than necessaryto 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 kΩpull-up
resistordrives the voltage at the resistor abovea TTL-low level of 0.4 VDC.
Figure 4-12 showsthe DIO configuration for high DIO power-up state.
Figure4-12. DIOChannel Configured for High DIO Power-upState with External Load
Example
Agiven DIO line is pulled high at power up. To pull it low on power up with
an externalresistor, follow these steps:
1. Installa load(RL). Rememberthat the smaller the resistance, the
greaterth e current consumption and the lower the voltage.
Device
DigitalI/O Line
82C55
100k
GND
RL
+5V