Instructions

UM-0085-B09 DT80 Range User Manual Page 332
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Digital Inputs
The DT80’s 8 digital I/O terminals (4 for DT81/82E) can be read individually, or can be read as 4 or 8 bit words.
The following channel types are used to read the states of digital inputs:
Channel Type
Valid Channel Numbers
Description
DS
1-8
(DT80/85)
1-4 (DT81/82)
Digital State: returns the state of digital input; 0=low, 1=high
DN
1-5 (DT80/85)
1
(DT81/82)
Digital Nybble
: returns the state of four consecutive digital inputs starting at the specified
input as a 4-bit number (0-15). The specified input will form the least significant bit of the
result.
DB 1
Digital Byte: returns the state of all eight digital inputs as an 8-bit number (0-255). Input
1D is the least significant bit.
For example, if channel 3DN returns the value 13 (binary 1101) then this indicates that input 3D (lsb) is high, 4D is low,
5D is high and 6D (msb) is high
Channel Options
The following channel options are applicable to digital input channel types:
• channel factor: for the multi-bit channel types (
DN, DB), the channel factor is a bitmask which specifies which
digital inputs to read. The default values for
DN and DB are 15 and 255 respectively (i.e. read all bits)
For example, 2DN(7) (bitmask = 0111 binary) will return the state of inputs 2D, 3D and 4D in bits 0 (lsb), 1 and 2
respectively. For input 5D the mask bit is zero so it is not read and bit 3 (msb) of the returned value will always be zero.
5D can then be used as an output if desired, e.g.
2DN(7) simultaneously read inputs 2D, 3D, 4D
5DSO=1 drive 5D as an output
Connecting to Digital Inputs
The two groups of digital input channels have different electrical characteristics. In particular:
• Inputs 1D-4D (1D-3D for DT81/82E) include a 47k pull-up resistor. The default state (if nothing is connected) is
therefore high. This in turn means that channels 1..4DS will return 1 if the inputs are not connected.
• Inputs 5D-8D (4D for DT81/82E, none for DT82I) include a 200k pull-down resistor. Their default state is
therefore low (0). So if all 8 inputs are disconnected then
1DB will return 15 (00001111).
Warning: The DT80’s digital inputs are not reverse-polarity-protected. Therefore ensure signal polarity is correct — positive to
numbered terminals, negative to DGND terminals — before connecting signals to the DT80’s digital inputs.
Do not apply more than 30Vdc to inputs 1D-4D (1D-3D for DT81/82E), and do not apply more than 20Vdc to inputs 5D-8D
(4D for DT81/82E).
DI1 – Relay Inputs
Voltage-free relay contact closures can easily be detected on channels 1D-4D (1D-3D for DT81/82E) by wiring the relay
contacts between the input pin and DGND, as shown below.
Channels 5D-8D (4D for DT81/82E) are less suitable for relay contact inputs, but they can still be used, for example if the
contacts are wired between the input pin and an external 3-20V dc supply (or one of the DT85/DT80 Series 2-4’s power
outputs, 12V or PWR OUT).
Figure 155: Wiring for reading contact closures on digital inputs
To measure
Use the command
state
1DS (0 = contacts closed, 1 = contacts open)