Modbus-Rtu - Omron CJ - REFERENCE MANUAL 07-2009 Reference Manual

Communications Frames
Response Frame
3-7-2

Modbus-RTU

Command Frame
Note CompoWay/F commands use ASCII as the transmission code. Therefore, be
sure to use ASCII for the CompoWay/F command after the FINS command
code 2803 hex (from node number to text) using CMND(490) or other instruc-
tion.
Example: If the CompoWay/F command MRC SRC is "01" "02" (where the
quotation marks (" ") indicate ASCII characters), 0, 1, 0, 2 must be treated as
ASCII characters. Therefore, set "01" as 3031 hex (not 01 hex), and "02" as
3032 hex (not 02 hex).
Further, to write the CompoWay/F command to the command storage area
using CMND(490) in frame order (without creating empty bytes), the SID com-
ponent of the CompoWay/F command requires 1 byte of ASCII as 30 hex, so
the subsequent components (s+3 and afterwards) must be set in one byte
each.
Frame before Conversion
STX Node No. Sub-
1
(× 10 ) address
(02 hex)
(× 10 2 )
"00"
(ASCII (ASCII
code code
4 bytes) 3030
hex) etc.
Frame after Conversion
FINS header FINS command
Remote Remote Remote MRC
unit ad-
network node
dress
address address
(DA2)
(DNA) (DA1)
etc.
Serial 00 hex Serial 28
port port unit
allocated address
address
Frame before Conversion
FINS header
Remote Remote Remote
network node unit
address address address
(DNA) (DA1) (DA2)
Serial port 00 hex Serial
allocated port
address unit
address
or local or local
network network
address node
address
Frame after Conversion
Start (silent Slave
interval of
address
3.5
(1 byte)
characters)
(See note.)
Note The silent interval in the Modbus-RTU frame is automatically generated by the
Serial Communications Board/Unit.
CompoWay/F
End code Command Response Text ETX BCC
(MRC, (MRES,
(ASCII (ASCII (03 hex)
SRC) SRES)
code code)
(ASCII (ASCII
8 bytes)
code code
8 bytes) 8 bytes)
FINS end code
SRC MRES SRES
03 User- User- Node No. Sub-
(× 10 1 )
address
speci- speci-
(× 10 2 ) "00"
fied fied
(ASCII code
(ASCII code
3030 hex)
2 bytes) etc.
FINS command
Etc. MRC SRC
28 04 Slave
address
(1 byte)
Modbus-RTU frame
FUNCTION Communications data
code (n bytes)
(1 byte)
CompoWay/F
(See note.)
End code Command Response Text
(MRC, (MRES,
(ASCII (ASCII
SRC) SRES)
code code)
(ASCII (ASCII
2 bytes)
code code
4 bytes) 4 bytes)
Modbus-RTU
(command section only)
FUNCTION Communications data
code(1 byte) (n bytes)
Error End (silent
interval of
check
3.5
CRC
characters)
(1 byte)
(See note.)
Section 3-7
87