User Manual

66 MODBUS Programmable I/O NA-9379 FnIO S-Series
Copyright(C) CREVIS Co.,Ltd Support [phone] URL : www.crevis.co.kr
A.3.7. 8 (0x08) Diagnostics
MODBUS function code 08 provides a series of tests for checking the communication system between a client
(Master) device and a server (Slave), or for checking various internal error conditions within a server.
The function uses a two–byte sub-function code field in the query to define the type of test to be performed. The
server echoes both the function code and sub-function code in a normal response. Some of the diagnostics cause
data to be returned from the remote device in the data field of a normal response.
• Request
Field name
Example
RTU
ASCII
ASCII (bus line)
Start of Frame
-
t1-t2-t3
“,”
0x3A
Slave Address
0x07
0x07
“07”
0x30, 0x37
Function Code
0x08
0x08
“08”
0x30, 0x38
Sub-Function Hi
0x00
0x00
“00”
0x30, 0x30
Sub-Function Lo
0x00
0x00
“00”
0x30, 0x30
Data Hi
0x11
0x11
“11”
0x31, 0x31
Data Lo
0x22
0x22
“22”
0x32, 0x32
Error Check (CRC/LRC)
-
0x6C, 0x24
“BE”
0x42, 0x45
End of Frame
-
t1-t2-t3
CR, LF
0x0D, 0xA
• Response
Field name
Example
RTU
ASCII
ASCII (bus line)
Start of Frame
-
t1-t2-t3
“,”
0x3A
Slave Address
0x07
0x07
“07”
0x30, 0x37
Function Code
0x08
0x08
“08”
0x30, 0x38
Sub-Function Hi
0x00
0x00
“00”
0x30, 0x30
Sub-Function Lo
0x00
0x00
“00”
0x30, 0x30
Data Hi
0x11
0x11
“11”
0x31, 0x31
Data Lo
0x22
0x22
“22”
0x32, 0x32
Error Check (CRC/LRC)
-
0x6C, 0x24
“BE”
0x42, 0x45
End of Frame
-
t1-t2-t3
CR, LF
0x0D, 0xA