YOKOGAWA UTAdvanced Series, User Manual

Page: 35 / 866

3-4
IM 05P07A01-01EN
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Specifying D registers / I relays
When you use a commercially available SCADA or the like or a user-created
communication program, you must be careful when specifying D register / I relay
numbers contained in messages because in both cases, you cannot use the original D
register / I relay numbers as they are.
When using a commercially available SCADA or the like:
Specify D register numbers by changing them into reference numbers. To change
them into a reference number, replace the D register number's leading character “D”
with “4.”
Specify I relay numbers by changing them into reference numbers. To change them
into a reference number, remove the I relay number's leading character “I.”
In a user-created communication program:
Specify D register numbers using the hexadecimal number of the value obtained by
subtracting “40001” from the D register's reference number.
Specify I relay numbers using the hexadecimal number of the value obtained by
subtracting “1” from the I relay’s reference number.
Example:
When specifying “D2018”:
• In SCADA, specify the reference number “42018.”
• Specify the message in the user-created communication program as “07E1”. This
number is the number “2017” (number obtained by subtracting 40001 from the
reference number) expressed in hexadecimal number.
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Error check
The error checking of the ASCII mode is different from the RTU mode.
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ASCII mode
In the ASCII mode, error checking is performed by the longitudinal redundancy check
(LRC).
Each individual byte from the communication address up to the final data (excluding “:”,
“CR” and “LF” ) is added, and the 2's complement of the result becomes LRC.
Ignore the uppermost carry during addition.
Example:
How to calculate the LRC in the case of command [:]110307E10004[LRC][CR][LF]
for reading four values continuously from D register D0218 of the controller at
communication address 17.
(1) Communication address 17 is expressed as “0x11” in Hex.
D2018 is “0x07E1”. This is the number “2017” (number obtained by subtracting
40001 from reference No. 42018) expressed in Hex.
When this is converted to 1-byte Hex data, this becomes “11,03,00,C8,00,04”.
(In Modbus/ASCII messages, “11” is ASCII code “H’ 31, H’ 31”, which comprises
two bytes.)
(2) This 1-byte Hex data is added one byte at a time as follows:
→ 11+03+07+E1+00+04 = 00
(3) 2's complement of the lowermost 1 byte of the result of addition is “00”.
00000000 (0x00) → 11111111 (complement) +1=00000000 (00)
3.1 Modbus Communication