Wire Transmission
Twisted pair using differential signaling with a signaling speed of 9600 bit/s. Ideal wave resistance at 100 kHz is 120 Ω. Line resistance at 20 Ω/km, max 75 Ω/km. Maximum capacitance bus-to-bus line max 800 pF/m at 800 Hz. Higher capacitance requires proportionally shorter cable length. Bus power with 30 V DC and 25 mA Polarization critical. Devices within same physical segment are addressed with 8-bits Maximum 57600 network nodes. Media access control is controlled with the CSMA/CA method. Maximum segment length is 1000 m. 4 segments may be connected with line repeaters to establish a network length of 4000 m. Loops are not allowed.
| # | Field | D7 | D6 | D5 | D4 | D3 | D2 | D1 | D0 |
|---|---|---|---|---|---|---|---|---|---|
| 0 | Control R-repeated packet Px-priority |
1 | 0 | R | 1 | P1 | P0 | 0 | 0 |
| 1 | Source address #0 | ||||||||
| 2 | Source address #1 | ||||||||
| 3 | Destination address #0 | ||||||||
| 4 | Destination address #1 | ||||||||
| 5 | Destination type Routing info Length |
DT | R2 | R1 | R0 | L3 | L2 | L1 | L0 |
| 6 | User data 1-16 bytes | ||||||||
| Checksum (S) |
If the destination type flag (DT) is set the packet will be multicast or broadcast. R2-R0 is decremented for each routing hop, like TTL in IP. L3-L0 correspond to 1-16 user data bytes. Source is always a physical address. Destination may be either a physical or group address. Logical “0” is defined as impulse under the reference level 30 V DC. Logical “1” is lack of the same impulses.
There exist an alternative interface speed at 4800 bit/s taken over from BatiBUS. But KNX TP-0 products will only operate on the same network. But not be able to exchange information with BatiBUS devices.
Read more about this topic: KNX (standard)
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