Signal Level Control - Measurement Computing PCI-DIO24 User Manual

PCI-DIO24 User's Guide

Signal level control

All I/O bits are set to a high impedance input mode on power up and reset. To prevent unwanted signal levels,
and to drive all inputs on the device you are controlling to a known state after power up or reset, install pull-up
or pull-down resistors.
A pull-up resistor pulls all digital pins up to +5 V (high logic level). A pull-down resistor pulls all digital pins
down to 0 V (low logic level).
The PCI-DIO24 has open locations where you can install a 2.2 K , eight-resistor single inline package (SIP)
resistor network for each port. The SIP is made up of eight 2.2 K resistors. One side of each resistor is
connected to a single common point and brought out to a pin. The common line is marked with a dot or line at
one end of the SIP. The remaining resistor ends are brought out to the other eight pins (see Figure 5).
Install the SIP on the PCI-DIO24 board at the locations labeled PORT A, PORT B and PORT C (adjacent to
the 37-pin connector). Figure 6 shows a schematic of an SIP installed in both the pull-up and pull-down
positions.
+5 VDC
COM
HI
n7
n6
n5
Digital n4
I/O Port
n3
n2
n = A, B, or C
n1
n0
LO
(GND)
2.2 K SIP installed for pull-up
Dot
(L O or HI)
Figure 5. Eight-resistor SIP schematic
Dot indicates the
2.2 K SIP
common line
Figure 6. Pull-up and pull-down resistor SIP schematic
2.2K Ohm SIP
I/O Lines
+5 VDC
n7
n6
n5
Digital
n4
I/O Port
n3
n2
n = A, B, or C
n1
n0
LO
(GND)
2.2 K SIP installed for pull-down
13
Functional Details
2.2 K SIP
HI
COM
Dot indicates the
common line