YOKOGAWA UTAdvanced Series, User Manual

Page: 36 / 866

3-5
IM 05P07A01-01EN
Description of RS-485 Communication (for UT
Advanced with RS-485 Communication)
3

RTU Mode
In the RTU mode, error checking is performed by the cyclic redundancy check
(CRC-16). Of all message blocks (from communication address through to final
data), eight bits (excluding start bit, stop bit and parity bit) are aligned serially, and
the remainder (16 bits) when the result is divided by predetermined binary 17 bits
becomes the CRC-16.
Example (CRC-16 calculation example)
When reading four data from D register D2018 by function code 03 (read status of
multiple D registers) from the slave at communication address 11 (0Bh).
“0B0307E10004” is sent as the send command.
(1) Default is FFFF. This is XORed (exclusive ORed) with the 1st byte (= slave address
11).
(2) The lower byte of the result is referenced, and the value corresponding to that
value in the following table is obtained. In this case, the 244th value in the table is
referenced to obtain 8701h as the result is F4h.
(3) The upper byte of the result of the XOR in (1) is XORed with the result of (2).
(4) The result (remainder) of (3) is taken as the next default, and the same operation is
performed on the 2nd byte (=function code 03).
Default value FF FF
Communication address 0B
---------
XOR FF F4
Reference to table 87 01
--------
XOR 87 FE
Function code 03
--------
XOR 87 FD
Reference to table 81 C1
--------
XOR
•
•
• •
•
•
81 46
XOR 14 78
Last character 04
--------
XOR 14 7C
Reference to table E1 01
--------
Resulting error E1 15
Convert the hex value to a decimal
value, find the corresponding number
in table of next page (Table Showing Results
of Error Checking (CRC) of Values 0 to 255
by A001h), and substitute the number
into the formula.
In the example shown on the left,
hex value “F4” is converted to decimal
value 244. From table of next page, the number
corresponding to 244 proves to be “8701”.
This number is substituted into the formula.
(5) From here on, steps (1) to (4) are repeated to calculate up to the final “04”.
(6) The upper and lower bytes of the result of calculation “E115” are inverted, and “15E1”
is appended to the final.
0B0307E1000415E1
3.1 Modbus Communication