Page 23 - Serial Data Transmission and KNX Protocol

KNX TUTOR SEMINAR

Character frame

4
0 1.352 t / ms

ST Start bit
SP Stop bit
D0 to D7 Character bits
P Parity bit
t 4 Delay between two characters (2 bit pulses)
The protocol foresees a transmission break t of at least one character width after the
2
sending of the entire telegram. The next character width is reserved for the reception of
acknowledgement, which must be sent by the addressed bus devices of the link or of the
line coupler / backbone coupler / line repeater.

A bus idle time t of 50 bit pulses is observed after the transmission of the
3
acknowledgement (IACK, INACK or BUSY).

Packet Packet

t1 t2 t3 t / us

t1 Priority-dependent waiting time
t2 Delay between telegram and acknowledgement
t3 Bus idle time
Q Acknowledgement
The total time t tot required for the transmission of the telegram and the acknowledgement
and the observance of the bus idle time is calculated as follows:

t = t + t + ( n + 2 13) ∗ ∗ bitpulses,
3
1
tot
8
≤ ≤ 23
n
20 ms t≤ tot ≤ 40 ms

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