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3.4.3
Explanation of MODBUS ASCII Codes
■
The following codes from a) Start Code, b) Slave Address up to j) Error Number will be expressed in ASCII code:
■
See
for details about ASCII codes.
■
See
3.4.1 Structure of MODBUS ASCII Request Message (Data Transmission from the Upper Computer to This Product)
”
for the
conversion to ASCII codes.
a) Start Code
This is a code that is necessary for the receiving side to detect the start of the message. It shall be attached to the start of
the character string to be sent.
b) Slave Address
This is the address of the device that will be communicated by the upper computer (this product).
The address in the response message from this product indicates the source of the response message.
c) Function Code
Enter the code 03H or 10H.
・
03H: If the data is to be read from this product
・
10H: If the data is to be written or saved into this product
d) Register Address
Specifies the position of data to be read or written with two bytes.
See
“
6. List of Identifiers (Codes)
”
for the address of each command.
e) Number of Registers
Specifies the number of registers that write.
Since the number of registers of this product is fixed to 2, set it to
“
0002H
.”
f) LRC
This is an error checking code for the detection of possible errors in the message. It sends LRC.
LRC that is used in this product is a value where all data in the message, except for start code and end code, are
summed up without performing a carryover and treat the sum total as a complement of 2.
Any portion that is expressed as
“
1
”
and
“
B
”
shall be considered as
“
1BH
.”
If 12H was computed as an error number, attach
“
1
”
and
“
2
”
at the end of the message.
g) End Code
This is a code that is necessary for the receiving side to detect the end of the message.
CR(0DH) and LF(0AH) shall be attached at the end of the character string to be sent.
h) Number of Bytes
Specifies the number of registers that read and write x 2.
Since the number of registers of this product is 2 (fixed), set
“
04H
.”
