Measurement Computing USB-201-OEM - Manual (Page 11)

USB-201-OEM User's Guide Functional Details
11
Digital I/O
You can connect up to eight digital I/O lines to DIO0 through DIO7 . The digital I/O terminals can detect the
state of any TTL-level input. Refer to the schematic shown in Figure 5.
Figure 5. Schematic showing switch detection by digital channel DIO0
If you set the switch to the +5 V input, DIO0 reads TRUE (1). If you move the switch to GND, DIO0 reads
FALSE (0).
Internal pull-up/down configuration
The digital port has 47
kΩ resistors that you can configure as pull-up or pull-down with an internal jumper.
Unconnected inputs are pulled low by default to 0 V through 47
kΩ resistors. The pull-up/pull-down voltage is
common to all 47
kΩ resistors. You can change the configuration with an internal jumper; see Figure 2 on page
9 for the location this jumper.
Caution! The discharge of static electricity can damage some electronic components. Before handling the
board, either ground yourself using a wrist strap or touch the computer chassis or other grounded
object to eliminate any stored static charge.
Figure 6 shows the jumper configured for pull-down.
Figure 6. Pull-down jumper
Configure the jumper for pull-up to pull the digital inputs high (+5V).
Trigger input
The TRIG terminal is an external digital trigger input. The trigger mode is software-selectable for edge- or
level-sensitive.
Counter input
The CTR terminal is a 32-bit event counter that can accept frequency inputs up to 1 MHz. The internal counter
increments when the TTL levels transition from low to high.
Voltage output
The user voltage output (+VO) terminal can output up to 100 mA maximum at approximately +5V. You can use
this terminal to supply power to external devices or circuitry.
Caution! The
+VO terminal is an output. Do not connect to an external power supply or you may damage
the device and possibly the computer.
Ground
The analog ground ( AGND ) terminals provide a common ground for all analog channels. The digital ground
( GND ) terminals provide a common ground for the digital, counter, pacer I/O, and power terminal.