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9.4 EIA-485 Bus Protocol
The data protocol describes the access method according to the Master-Slave-
principle via a serial EIA-485 bus. This also comprises the point-to-point connection.
Features:
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You can connect one master and a maximum of 31 slaves to the bus. The single
slaves are selected by the master via an address character. An IGM11 can never take
the transmission initiative automatically. The communication is carried out in half-
duplex operation.
9.4.1 Telegram Syntax
Each telegram begins with the starting signal STX (Start of Text, 0x02h), followed by
the length specification (LNG) and the address byte (ADR), after that the user data.
The telegram ends with checksum (Block Check Character).
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Strict support of the USS protocol by Siemens (USS is a trademark of the
Siemens AG)
Support of a multipoint connection via the EIA-485 hardware
Master-slave access method
Single master system
Maximum of 32 nodes (max. 31 slaves)
Simple, secure telegram frame
Simply feasible
Figure 26 EIA-485 Telegram Syntax
Gaussmeter IGM11 Operating Instructions
Chapter 9 Serial Interfaces
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