Data Sheet

QPRO Technical Data Sheet
Document 1137-0901, REV K 22
The example below will scale a 0-20mA sensor to 0-3.5 VDC at the input to the modem .
Figure 4-4, Sample 24V Sensor
4.1.2 Digital Inputs/Outputs
The Q4000 has eight general purpose digital CMOS (3.3VDC) level inputs/outputs. The DIO’s are located on
pins 33 - 39 of the 40-pin interface connector. The DIO’s may be configured as inputs or outputs, set and
cleared and read by software. As seen below in Error! Reference source not found., there are no internal
pull up or pull down resistors.
Figure 4-5, Digital Input Circuit
4.1.2.1 DIO as Input
When utilized as an input, a logic level “high” is obtained when the input voltage is greater than 2.2 VDC. It
remains in this asserted state until the voltage on the pin falls below .8 Volts where a valid logic level “low” is
read. This hysteresis prevents noise on the input pin from causing the input to jitter.
4.1.2.2 DIO as Output
When used as an output, the voltage/current provided is dependent on the impedance or load presented on
the line.
• For voltage use the 10K ohm resistor works against the line impedence (R LINE ) and VOUT is as
follows:
VOUT = 3.5 * R LINE / (10,000+R LINE )
• For Current usage the 10K ohm drops voltage across it as the current is increased. The output
voltage follows the current draw ( I LOAD ) as follows:
VOUT = 3.5 – (I LOAD * 10,000)
10K
1%
100PF
50V
100PF
50V
3.9V ZENER
DIGX_IF
> 1M
Microcontroller
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