Measurement Computing PCI-DIO24/S - Manual (Page 13)

PCI-DIO24/S User's Guide Functional Details
13
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 outputs 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).
Each board 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).
2.2 KOhm SIP
Dot
(LO or HI)
I/O Lines
Figure 5. Eight-Resistor SIP Schematic
Each port provides 10 holes. Install an SIP on the board at the locations labeled Port A , Port B and Port C (see
Figure 6).
Pull-up / pull-down
resistor locations
Figure 6. Pull-up/down resistor locations
The end labeled HI connects to +5 V. The end labeled LO connects to GND. The eight holes in the middle (n0 –
n7) connect to the eight lines of the port (Port A, B, or C). Figure 7 shows an SIP resistor network installed in
both pull-up and pull-down positions.