Thermo Scientific 49i Instruction Manual page 300

MODBUS Protocol
Function Codes
C-4 Model 49i Instruction Manual
The outputs in the response message are packed as one per bit of the data
field. Status is indicated as 1 = Active (on) and 0 = Inactive (off ). The LSB
of the first data byte contains the output addressed in the query. The other
outputs follow toward the high order end of this byte, and from low order to
high order in subsequent bytes. If the returned output 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.
Note The values reported may not reflect the state of the actual relays in the
instrument, as the user may program these outputs for either active closed or
open.
Request
Function code 1 Byte
Starting Address 2 Bytes
Quantity of outputs 2 Bytes
Unit Identifier 1 Byte
Response
Function code 1 Byte
Byte count 1 Byte
Output Status n Byte
*N = Quantity of Outputs / 8, if the remainder not equal to zero, then N=N+1
Error Response
Function code 1 Byte
Exception code 1 Byte
Here is an example of a request and response to read outputs 2–15:
Request
Field Name (Hex)
Function 0x01
Starting Address Hi 0x00
Starting Address Lo 0x02
Quantity of Outputs Hi 0x00
Quantity of Outputs Lo 0x0D
0x01 or 0x02
0x0000 to maximum allowed by instrument
1 to maximum allowed by instrument
0x00 to 0xFF (Passed back in response)
0x01 or 0x02
N*
n = N or N+1
Function code + 0x80
01=Illegal Function, 02=Illegal Address,
03=Illegal Data, 04=Slave Device Failure
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