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Function Code
Function Codes
(0x01/0x02) Read Coils /
Thermo Fisher Scientific
The function code is a single byte in length. The following function codes
are supported by the instrument:
Read Coils
Read Inputs
Read Holding Registers
Read Input Registers
Force (Write) Single Coil
Read Exception Status
If a function code is received that is not in this list, and invalid function
exception is returned.
Data
The data field varies depending on the function. For more description of
these data fields, see "Function Codes" below.
Error Check
In MODBUS over Serial an error check is included in the message. This is
not necessary in MODBUS over TCP/IP because the higher-level protocols
ensure error-free transmission. The error check is a two-byte (16-bit) CRC
value.
This section describes the various function codes that are supported by the
Model 43i Trace Level-Enhanced.
Read Coils/Inputs reads the status of the digital outputs (relays) in the
instrument. Issuing either of these function codes will generate the same
Read Inputs
response.
These requests specify the starting address, i.e. the address of the first
output specified, and the number of outputs. The outputs are addressed
starting at zero. Therefore, outputs numbered 1 – 16 are addressed as 0 – 15.
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
:
0x01
:
0x02
:
0x03
:
0x04
:
0x05
:
0x07
Model 43i Trace Level-Enhanced Instruction Manual
MODBUS Protocol
Function Codes
C-3
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Troubleshooting
