Thermo Scientific 5028i Instruction Manual page 307

Function Code
Error Check
Function Codes
(0x01/0x02) Read Coils/
Read Inputs
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, an invalid function
exception is returned.
The data field varies depending on the function. For more description
Data
of these data fields, see "Function Codes" below.
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 5028i.
Read Coils/Inputs read the status of the digital outputs (relays) in the
instrument. Issuing either of these function codes will generate the same
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 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.
MODBUS Protocol
: 0x01
: 0x02
: 0x03
: 0x04
: 0x05
: 0x06
Model 5028i Instruction Manual
Function Codes
C-3