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4 Modbus Communications Procedure
4-4
Detailed Description of the Functions
4-4-1 Variable Read, Multiple
To read from the variable area, set the required data in the command frame, as shown in the following
diagram.
Command Frame
Slave
Function
address
code
H'03
1
1
Name
Slave address
Function code
Read start address
Number of elements
CRC-16
4 - 8
Number of
Read start address
Elements
2
2
Specify the E5@D's unit number.
The unit number can be set between H'01 and H'63 hexadecimal (1 to 99 decimal).
The Read Variable Area function's function code is H'03.
Specify the address containing the data to be read.
Refer to Section 5 Communications Data for Modbus for details on addresses.
4-byte Mode
Specify 2 times the number of setting data items as the number of elements to be
read. The setting range for the number of elements is H'0002 to H'006A (2 to 106).
When H'006A is set, 53 items of setting data can be read.
Example: When reading 2 items of setting data, set the number of elements to
H'0004.
2-byte Mode
Specify the number of setting data items to be read as the number of elements.
The setting range for the number of elements is H'0001 to H'006A (1 to 106).
When H'006A is set, 106 items of setting data can be read.
Example: When reading two items of setting data, set the number of elements to
H'0002.
This check code is calculated with the data from the slave address to the end of the
data.
For details on the CRC-16 calculation, refer to CRC-16 Calculation Example in 4-1-1
Command Frame on page 4-2.
E5@D Digital Temperature Controllers Communications Manual (H225)
CRC-16
2 bytes
Description
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