Measurement-computing BTH-1208LS Manuel d'utilisateur télécharger pdf (Page 17)

BTH-1208LS User's Guide Functional Details

Digital I/O

You can connect up to eight digital I/O lines to DIO0 through DIO7. When configured for input, the digital

terminals can detect the state of any TTL-level input.

Digital input voltage ranges of up to 0 to 5.5 V are permitted, with thresholds of 0.8 V (low) and 2.0 V (high).

Each DIO channel is an open-drain, which can sink up to 50 mA for direct drive applications when used as an

output.

Figure 5 shows an example of a typical digital output connection.

Figure 5. Digital output connection (typical)

External pull-up capability

Inputs are pulled high by default to 3.3 V through 47.5 kΩ resistors on the circuit board. The pull-up voltage is

common to all 47.5 kΩ resistors.

You can place an external pull-up resistor on any of the DIO bits in order to limit source current to less than

50 mA., which requires a 100 Ω resistor minimum. A 2 kΩ or 5 kΩ resistor would be typically used, allowing

for a 1 mA current

You can also use an external pull-up resistor to pull the DIO bit up to a voltage that exceeds the internal 3.3 V

pull-up voltage (5.5 V maximum).

When using external pull-up resistors, be aware that the internal resistors cause a slight voltage shift to digital

lines in the on state as various lines change between the on/off states.

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Measurement-computing BTH-1208LS Manuel d'utilisateur Page 17