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D20/D200 Technical Overview
2.4.6 D20S Digital Input Peripheral
The D20S Digital Input Peripheral, illustrated above, obtains and processes digital input states
from field devices. Changes of state in the digital inputs are reported to the D20 main processor
for further processing, over the high-speed D.20 Link.
Note: D20C peripherals are also able to process digital inputs. Digital input processing on the
D20C is the same as that on the D20 S. More information on the D20C is provided in
section 2.4.10 , D20C Combination I/O Peripheral.
The D20S logic module plugs directly into a D20S termination panel equipped with screw
compression type terminals for field terminations. The D20S termination panel is jumper
configurable, so that contact wetting can be supplied from either the D20S power source or from
an external source. Wetting voltage is fused and monitored.
The D20S can accept up to 64 digital inputs, each of which can be configured from a
downloaded database to be processed as one of the following:
• Status and alarm inputs
• Status inputs with change of state detection (COS)
• Sequence of events (SOE) using time-tagged COS
• Binary-Coded Decimal or parallel inputs
• Pulse accumulator or counter inputs
• Pulse duration inputs.
The 64 digital inputs are organized in eight groups of eight electrically isolated inputs, each
group with a common return. Each input is photo coupled and can accept inputs of 24, 48 or 130
V DC of any polarity. The microprocessor scans each input at one millisecond intervals and
provides selectable debounce of 4 to 255 ms. Changes are time-tagged to a resolution of one
44
Figure 28 D20S Digital Input Peripheral
PRPI-019-3.00-10
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