Rabbit OP7100 User Manual download pdf (Page 26)

20 eDisplay (OP7200)

3.3 Digital I/O

3.3.1 Digital Inputs

The OP7200 has 19 digital inputs, IN0–IN18, each of which is protected over a range of

–36 V to +36 V. The inputs are factory-configured to be pulled up to +5 V, but they can

also be pulled down to 0 V in banks of eight by changing a surface-mounted 0 Ω resistor.

Figure 7 shows a sample digital input circuit. All 19 inputs are protected against noise

spikes by a low-pass filter composed of a 22 kΩ series resistor and a 10 nF capacitor.

Figure 7. OP7200 Digital Inputs [Pulled Up—Factory Default]

OP7200 series boards can be made to order in volume with the banks of digital inputs

pulled down to 0 V. Contact your authorized Rabbit distributor or your Rabbit sales

representative for more information.

For IN0–IN7 the actual switching point between a zero and a one is 1.5 V max and 3.5 V

min respectively. The range between 1.5 and 3.5 V is undefined. For IN8–IN15 the actual

switching point between a zero and a one is 0.8 V max and 2.0 V min respectively. The

range between 0.8 and 2.0 V is undefined. For IN16–IN17, which are available only on

the OP7200 model, the actual switching point between a zero and a one is 0.8 V max and

3.5 V min respectively. The range between 0.8 V and 3.5 V is undefined.

Therefore, the input voltage must be less than 0.8 V for all the digital inputs as a group to

ensure that a zero is being read, and the input voltage must be must be greater than 3.5 V

for a one.

IN16–IN18 interface to the A/D converter chip serially with an access time of 100 µs,

which is different from the access time of 5 µs for IN0–IN15, which interface in parallel

with the Rabbit 2000 microprocessor.

10 nF

22 kW

27 kW

Rabbit 2000

Microprocessor

Factory

Default

Vcc

GND

0 W

JP3

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Rabbit OP7100 User Manual Page 26