User Manual

Figure 2-5. IO used to detect the state of a switch.

While providing overvoltage/short-circuit protection, the 1.5 k Ω series resistor on each IO pin

also limits the output current capability. For instance, with an output current of 1 mA, the series

resistor will drop 1.5 volts, resulting in an output voltage of about 3.5 volts.

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 IO pin. Both of these functions take up to 20 ms to execute, providing a

maximum update rate of about 50 Hz per pin.

The function AISample can set/read the state of each IO, and the function Counter reads the

state of each IO.

The functions AIBurst and AIStreamRead, take a reading of the IO states and return it with the

analog data. The states of the 4 IO are read simultaneously every 4 samples, providing a data

rate of up to 2048 Hz per pin for burst mode, or 300 Hz per pin for stream mode.

2.4 D0 – D15

Connections to 16 of the LabJack’s 20 digital I/O are made at the DB25 connector, and are

referred to as D0-D15. These 16 lines have no overvoltage/short-circuit protection, and can

sink or source up to 25 mA each (total sink or source current of 200 mA max for all 16). This

allows the D pins to be used to directly control some relays. All digital I/O are CMOS output and

TTL input except for D13-D15, which are Schmitt trigger input. Each D pin has a 10 MΩ resistor

connected to ground.

DB25 Pinouts:

1: D0 6: D5 11: +5V 16: GND 21: D11

2: D1 7: D6 12: +5V 17: GND 22: D12

3: D2 8: D7 13: +5V 18: D8 23: D13

4: D3 9: NC 14: GND 19: D9 24: D14

5: D4 10: +5V 15: GND 20: D10 25: D15

These digital I/O can detect the state of a switch using the same circuit shown in Figure 2-5.

Because the D pins have no overvoltage/short-circuit protection, the user must be

careful to avoid damage. A series resistor can provide substantial protection for these

pins (see the CB25 datasheet). The following are examples of things that could damage

a D pin and/or the entire LabJack: