Transmission mode (RTU)
The transmission mode used is the RTU (remote terminal unit) mode. Data are trans- mitted in binary format (hexadecimal) with 8 bits.
The LSB (least significant bit) is transmitted first. ASCII mode is not supported.
Data format | The data format describes the structure of the transmitted byte. |
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| Data word | Parity bit | Stop bit ½ bit | Number of bits |
| 8 bit | Not | 1 | 9 |
Device address
The slaves’ device addresses can be selected between 1 and 99.
Device address 0 is reserved.
A maximum of 31 slaves can be addressed via the
There are 2 choices of data exchange:
Query | Data query / instructions delivered by the master to a slave via the re- |
| spective device address. |
| The addressed slave responds. |
Broadcast | Master instructions to all slaves via device address 0. |
| The addressed slaves do not respond. |
| A data query with device address 0 does not make sense. |
| A certain setpoint can be transmitted to all slaves, for example. |
| In that case, correct adoption of the value by the slaves should be |
| checked by subsequent setpoint readout. |
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Siemens Building Technologies | CC1A7865.1en |
HVAC Products | 31.10.2002 |
