Beijer Electronics NA-9379 - Manual (Page 66)

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MODBUS Programmable I/O NA-9379 FnIO S-Series
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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