Omega OME-ET-7000 Series, User Manual

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4.5.2. 02 (0x02) Read Discrete Inputs
This function code is used to read status of discrete inputs in an
OME-ET-7000/OME-PET-7000 module. The Request PDU specifies the starting
address, i.e. the address of the first input specified, and the number of inputs. In the
PDU Discrete inputs are addressed starting at zero.
The discrete inputs in the response message are packed as one input per bit of the
data field. Status is indicated as 1=ON and 0=OFF. The LSB of the first data byte
contains the input addressed in the query. The other inputs follow toward the high
order end of this byte, and from low order to high order in subsequent bytes.
If the returned input quantity is not a multiple of eight, the remaining bits in the final
data byte will be padded with zeros (toward the high order end of the byte). The Byte
Count field specifies the quantity of complete bytes of data.
Here is an example of a request to read digital inputs of
OME-ET-7026/OME-PET-7026 module:
Request Response
Field Name (Hex) Field Name (Hex)
MBAP Header
01
MBAP Header
01
02 02
00 00
00 00
00 00
06 04
Unit Identifier 01 Unit Identifier 01
Function Code 02 Function Code 02
Starting Address Hi 00 Byte Count 01
Starting Address Lo 00 Digital Inputs status 0-1 03
Quantity of Inputs Hi 00
Quantity of Inputs Lo 02
The status of Inputs 0-1 is shown as the byte value 03 hex, or binary 0000 00 11 . DI1
is in the seventh bit position from the left, and DI0 is the LSB of this byte. The six
remaining high order bits are zero filled.