XPS-E
22 / 36
Reception of a Modbus RTU
response telegram
After transmitting a Modbus RTU request telegram, XPS-E waits for
a response of the addressed Modbus slave. After the correct
reception of the response telegram it is forwarded without CRC to the
PROFIBUS DP Master. If no response is received within the
configured timeout (See Chapter„Send Data“ [
}
15], Section „Modbus
RTU-Master) XPS-E reports via the receive status byte a timeout
error to the PROFIBUS DP Master.
Byte
Telegram Element
Value Range (dec)
1
Receive status
0 – 255
2
Receive confirmation number of
XPS-E
0 – 255 (See Chapter„
R
eceive Data“
[
}
15])
3
Data size N of the following user data
0 – 237 (See Chapter
Receive Data“,
[
}
15]
Section „Modbus RTU
Master“).
4..4+N
Modbus Data
0 – 255
Table 10:
Structure of a Modbus RTU Response-Telegramm
The telegram buffer consists of 3 byte header and successive
Modbus specific application data (from byte 4).
– Byte 1:Receive status of the Modbus RTU response telegram (Bit set =
status active):
Bit
Meaning
0
Reserved
1
Reserved
2
Paritiy error
3
Receive data available
4
Reserved
5
Modbus request too large (max. PROFIBUS Output size-3)
6
Modbus response too large (max. PROFIBUS Input size - 3)
7
Modbus Timeout
Table 11:
Receive status of a Response-Telegram
Data exchange