Signal Level Control - Measurement Computing PCI-DIO24H User Manual

PCI-DIO24H 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-DIO24H has open locations where you can install a 2.2 KΩ, eight-resistor single inline package (SIP)
resistor network for each port. The SIP is made up of eight 2.2 KΩ 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
Install the SIP on the PCI-DIO24H board at the locations labeled
the 37-pin connector).
positions.
+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-up
When installed, the SIP establishes either a high or low logic level at each of the eight I/O lines on the port. At
each board location, A, B, and C, there are 10 holes in a line. The hole on one end is marked "HI" and is
connected to +5V. The other end is marked "LO" and is connected to GND. The eight holes in the middle
connect to eight lines of the port, A, B or C.
To pull-up lines, orient the SIP with the common pin (dot) toward the HI end; to pull-down, install the resistor
with the common pin in the LO hole.
Note:
We recommend using 2.2KΩ SIPs (MCC part number SP-K2.29C). Use a different value only if necessary.
Dot
(LO or HI)
Figure 4-2. Eight-resistor SIP schematic
Figure 4-3 shows a schematic of an SIP installed in both the pull-up and pull-down
Dot indicates the
2.2 K SIP
common line
COM
HI
Figure 4-3. Pull-up and pull-down resistor SIP schematic
2.2KOhm SIP
I/O Lines
,
PORT A PORT B
+5 VDC
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-down
4-2
Functional Details
Figure 4-2 ).
and (adjacent to
PORT C
2.2 K SIP
COM
Dot indicates the
common line