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Appendix
31
MODBUS RTU | SPI 3 | Trebing & Himstedt
Acknowledge telegram without fragmentation
Bit 7 …6 …5 …4 …3 …2 …1 …0
Byte 0
…n
…2
…1
DP Master
SPI 3
OUT
Bit 7 …6 …5 …4 …3 …2 …1 …0
Byte 0
…n
…2
…1
IN
0
Receive telegram (only toggle Bit 2 in Byte 0, specify telegram length in Byte 1, specify user data from Byte 2 onward)
1
Bit 7
1
…6 …5 …4 …3 …2 …1 …0
Byte 0
…n
…2
…1
OUT
Bit 7
1
…6 …5 …4 …3 …2 …1 …0
Byte 0
…n
…2
…1
IN
Receive telegram 1
Receipt telegram 1
0x02
A
B
Telegram length
User data
Bit 7
0
…6 …5 …4 …3 …2 …1 …0
Byte 0
…n
…2
…1
OUT
Bit 7
0
…6 …5 …4 …3 …2 …1 …0
Byte 0
…n
…2
…1
IN
Receive telegram 2
Telegram length
User data
Receipt telegram 2
2
Receive next telegram (only toggle Bit 2 in Byte 0, specify telegram length in Byte 1, specify user data from Byte 2 onward)
0x02
Z
Y
0
0
Request (DP Master)
Response (SPI 3)
Example original configuration
Request (DP Master)
Response (SPI 3)
Request (DP Master)
Response (SPI 3)