NCN5121
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50
Host Ctrl NCN5121 KNX Bus
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
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
0 0 0 1 0 n b a
U_Ackn.req
x x x x x x x x
Data Octet N
x x x x x x x x
CRC−CCITT Low Byte
x x x x x x x x
CRC−CCITT High Byte
re ce te 1
res
0 1 1
U_FrameState .ind
1 1 0 0 1 0 1 1
U_FrameEnd.ind
Figure 55. Receive Frame, All Modes, Frame End with MARKER, with CRC−CCITT
re (receive error): ‘1’ if newly received frame contained corrupted bytes (wrong parity, wrong stop bit or
incorrect bit timings)
ce (checksum or length error): ‘1’ if newly received frame contained wrong checksum or length which does not correspond
to the number of received bytes
te (timing error) : ‘1’ if newly received frame contained bytes whose timings do not comply with the KNX
standard
res (reserved) : Reserved for future use (will be ‘0’).
Remarks on Figures 50 to 55:
− x = don‘t care (in respect with KNX standard)
− See Tables 12 and 13 for more details on all the bits
− Code of U_FrameEnd.ind (0xCB) can also be part of the KNX frame content (Data Octet). To make a distinguish
between a data octet and U_FrameEnd.ind, NCN5121 duplicates the data content (if 0xCB). This will result in 2 bytes
transmitted to the host controller (two times 0xCB) corresponding to 1 byte received on the KNX bus.
Above is only valid if frame end with MARKER is enabled.
− See p53 for info on CRC−CCITT.
Slave Polling Frame Service
Upon reception and consistency check of the polling control byte, the control byte is send back to the host controller
(L_Poll_Data.ind). The host controller will send the slot number to the device (U_PollingState.req), followed by the polling
address and the polling state. At the same time the source address, polling address, slot count and checksum is received over
the KNX bus. If the polling address received from the KNX bus is equal to the polling address received from the host controller,
NCN5121 will send the polling data in the slot as define by U_PollingState.req (only if the slotcount is higher as the define
slot).
U_PollingState.req can be sent at any time (not only during a transmission of a polling telegram). The information is stored
internally in NCN5121 and can be reused for further polling telegrams if auto−polling function gets activated.
