User Manual

• Shorting a high output to ground (or any potential other than +5V).
• Shorting a low output to a nonzero voltage (such as +5V).
• Exceeding the voltage limits specified in Appendix A.
Software
The easy functions EDigitalIn or EDigitalOut are used to read or set the state of one digital line,
and both take up to 20 ms to execute.
The functions AOUpdate and DigitalIO are used to set the direction, set the state, and/or read
the state, of each D pin. In addition, DigitalIO also returns the current state of the direction and
output registers. Both of these functions take up to 20 ms to execute, providing a maximum
update rate of about 50 Hz per pin.
2.5 CNT
The input connection to the 32-bit counter is made at screw-terminal CNT. The counter is
incremented each time the voltage at CNT changes from less than 1 volt to greater than 4 volts,
and is capable of counting frequencies up to at least1 MHz.
Software
The functions ECount (easy function), AOUpdate, and Counter are used to reset or read the
counter. If a reset is specified, the counter is read first. All of these functions take up to 20 ms
to execute, providing a maximum update rate of about 50 Hz.
Counter readings can also be returned in stream mode (AIStreamRead) at up to 300 Hz.
2.6 CAL – STB
These terminals are used during testing and calibration.
The CAL terminal is an operational amplifier output of the LabJack U12’s 2.5 volt reference.
Accidental application of an overvoltage or transient such as ESD (electro-static discharge) can
damage this amplifier, and cause a failure of all analog inputs. In most cases, this terminal is
unused and can be physically shielded. As an alternative, a series resistor and zener diode can
be used to provide additional protection. A 5.6 volt zener such as the 1N4734 (Digi-Key part
number 1N4734ADICT-ND) can be connected directly to the screw terminals. The thin stripe
(cathode) goes to CAL and the other lead goes to a nearby GND. One end of the series resistor
connects to AOx and the other end connects to your signal wire (the series resistor is not
needed if nothing is connected to CAL). The resistor should be as large as possible (10 ohms
will help, 100 ohms is good, 1k ohms is very good), taking into account the voltage that will be
dropped across the resistor.
2.7 +5V
The LabJack has a nominal +5 volt internal power supply. Power can be drawn from this power
supply by connecting to the +5V screw-terminals, or the +5V pins on the DB25 connector. The
total amount of current that can be drawn from the +5V pins, analog outputs, and digital outputs,
is 450 mA for most desktop computers and self-powered USB hubs. Some notebook
computers and bus-powered hubs will limit this available current to about 50 mA.
2.8 GND
The GND connections available at the screw-terminals and DB25 connector provide a common
ground for all LabJack functions. They are all the same.