YOKOGAWA UTAdvanced Series, User Manual

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3-3
IM 05P07A01-01EN
Description of RS-485 Communication (for UT
Advanced with RS-485 Communication)
3
3.1.2 Configuration of Messages
The structure of messages sent to the UTAdvanced from the host computer is as follows:
(1) (2) (3) (4) (5) (6)
Element
Message start
mark
Address No
(ADR)
Function code Data Error check Message end
mark
Number of bytes in RTU mode None 1 1
2n (variable
length)
2 None
Number of bytes in ASCII
mode
1 2 2
4n (variable
length)
2 2
(1) Message start mark
This indicates the start of the message. A colon (:) is required only in the ASCII mode.
(2) Address No. (01 to 99)
This No. is for enabling the host computer to identify the UTAdvanced at the
communication destination.
(Individual UTAdvanced ID numbers are expressed in Hex in messages.)
(3) Function code (See “3.1.5 Messages and Responses.”)
The instruction (function code) from the host computer is specified.
(4) Data
The D register / I relay numbers, number of D registers / I relays, parameter values,
etc. are specified according to the function code. (These are expressed in Hex in
messages.)
Writing to string parameters is set in the word unit to enable writing to be performed.
However, although the string length of each string parameter is fixed, once 0x00 is
written, 0x00 is consistently written in the subsequent strings, but not displayed in the
indicator.
Example:
Condition
Content of D
register n
Content of D
register n+1
Content of D
register n+2
Content of D
register n+3 Display data
Status before writing
to string parameter 12 (0x3132)
34 (0x3334) 56 (0x3536) (0x0000) 12345678
Status after writing
to string parameter 12 (0x3132)
3 (0x3300) (0x0000) (0x0000) 123
(5) Error check
In the RTU mode, errors are checked by the cyclic redundancy check (CRC-16).
In the ASCII mode, errors are checked by the longitudinal redundancy check (LRC).
(6) Message end mark
This indicates the end of the message. “CR” and “LF” are required only in the ASCII
mode.

Message format for communication
Example: When setting the target setpoint “50.00,” the host computer sends the value
“1388” as message data which is a hexadecimal value of “5000” (50.00 excluding
the decimal point) (this is also true for setting 5.000 or 500.0).
Target setpoint: 50.00
Message data to be sent from the host computer: 1388 (hexadecimal value of 5000)
Message data: 1388
UTAdvanced side
Response data from
UTAdvanced : 1388
* The UTAdvanced determine the decimal point position for “5000” by
the decimal point position parameter setting (in this case, P.DP = 2).
3.1 Modbus Communication