NCN5121
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U_L_DataStart/DataCont/DataEnd only provides space for 6 index bits. Because an extended frame can consist out of
263 bytes, an index of 9 bits long is needed. U_DataOffset.req provides the 3 most significant bits of the data byte index. The
value is stored internally until a new offset is provided with another call.
Each transmitted data octet on the KNX bus will also be transmitted back to the host controller.
Each transmission is ended with a L_Data.con service where the MSB indicates if an acknowledgment was received or not.
When operating in SPI or UART 8−bit Mode, L_Data.con is preceded with U_FrameState.ind.
Depending on the activated features, a CRC−CCITT service and/or a MARKER could be included.
Next figures give different examples of send frames.
1 0 0 0 0 0 0 0
U_L_DataStart.req
Host Ctrl NCN5121 KNX Bus
x x x x x x x x
Control Byte
1 0 i i i i i i
U_L_DataCont.req
x x x x x x x x
Data Octet 1
0 0 0 0 1 i i i
U_L_DataOffSet.req
1 0 i i i i i i
U_L_DataCont.req
x x x x x x x x
Data Octet N
0 1 l l l l l l
U_L_DataEnd.req
x x x x x x x x
Checksum
x x x x x x x x
Control Byte
x x x x x x x x
Data Octet 1
x x x x x x x x
Data Octet N
x x x x x x x x
Checksum
x 0 r 1 p1 p0 0 0
L_Data.ind
x x x x x x x x
Data Octet 1
x x x x x x x x
Data Octet N
x x x x x x x x
Checksum
x x x x x x x x
Immediate Ackn
re ce te 1
res
0 1 1
U_FrameState.ind
x 0 0 0 1 0 1 1
L_Data.con
w
2.6ms silence
Figure 44. Send Frame, SPI or 8−bit UART Mode, Frame End with Silence, No CRC−CCITT
