2 Protocol description
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2.3 Device address
The device address of the slave can be set between 0 and 254. Device
address 0 is reserved.
There are two different forms of data exchange:
Query Data request/instruction by the master to a slave via the corresponding device
address.
The slave addressed responds.
Broadcast Instruction by the master to all slaves via the device address 0 (e.g. to transmit
a specific value to all slaves).
The connected slaves do not respond. In such a case, the correct acceptance
of the value by the slaves should be checked by a subsequent readout at each
individual slave.
Data request with the device address 0 is meaningless.
2.4 Timing of the communication
Start and end of a data block are marked by transmission pauses. The
maximum permitted interval between two consecutive characters is three
times the transmission time required for a single character.
The character transmission time (time required to transmit one single
character) depends on the baud rate and the data format used (stop bits and
parity bit).
For a data format of 8 data bits, no parity bit and one stop bit, this is:
character transmission time [ms] = 1000 * 9 bit/baud rate
For the other data formats, this is:
character transmission time [ms]
= 1000 * (8 bits+parity bit+stop bit(s)) bit/baud rate
A maximum of 31 slaves can be addressed via the RS485 interface.
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