Rabbit eDisplay, User Manual

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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 k
Ω
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 k W
27 k W
Rabbit 2000®
Microprocessor
Factory
Default
Vcc
GND
0 W
JP3