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 when it detects a falling
edge followed by a rising edge. This means that if you reset the counter while your signal is low, you will not get the first count until it
goes high-low-high. In situations where this first count is important, you should simply substract the initial count from the final count,
rather than doing a reset.
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 primarily used at the factory during testing and calibration.
CAL is a precision 2.5 volt reference, and can be used during normal operation, but care should be taken to observe the current
limits specified in Appendix A. The CAL pin is protected from ESD and overvoltage, but severe overvoltage (steady-state or
transient) can damage CAL, and result in the failure of all analog inputs.
STB has 2 purposes. One is to disable the watchdog as described in Section 4.35, and the other is to create a rectangular output
signal for testing. For the latter, if the U12 is streaming the STB frequency matches the sampling frequency, while if not streaming
the STB frequency is about 28 kHz. To get this output signal on STB use the enableSTB parameter in the Counter function.
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.
The USB specification requires all hosts and hubs to have overcurrent protection. If the user puts too large a load on +5V
(including a short circuit of +5V to GND) of the LabJack U12 (a USB device), the host or hub is responsible for limiting the current.
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.
Caution should be used whenever making connections with systems that have their own power source. It is normal to connect U12
ground to other grounds to create a common reference, but the risk is that the U12 ground will become the preferred ground for the
other systems and they could try to send high currents into the U12. To prevent this it is often a good idea to put a 10-100 ohm
resistor (or even a fuse) in series with GND on the U12 and any grounds from active systems.
2.9 - OEM Versions
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