Serial interfaces
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IRDH275_D00122_02_M_XXEN/10.2016
7.4 BMS protocol (IRDH275B)
This protocol is an essential part of the Bender Measuring Device Interface.
Data transmission generally makes use of ASCII characters.
Interface data are:
• Baud rate: 9600 baud
• transmission: 1 start bit, 7 data bits, 1 parity bit, 1 stop bit (1, 7, E, 1)
• Parity: even
• Checksum: sum of all transmitted bytes = 0 (without CR and LF)
The BMS bus protocol works according to the MASTER-SLAVE principle. That
means that one device represents the MASTER while all other bus nodes are
SLAVES. It is important that only one MASTER is present in each network. All
bus nodes are identified by a unique address. The MASTER scans all other de-
vices on the bus cyclically, listens to their signals and then carries out specific
commands. Bus address 1 must be assigned to the Master, thus to one of the
IRDH275B devices.
7.4.1 BMS Master
A Master can query all warning and operating messages from a slave.
If the bus address 1 has been selected for one IRDH275B, this device automat-
ically represents the Master, that means that all addresses between 1 and 150
are cyclically scanned via the BMS bus for alarm and operating messages. If
the Master receives no answer from five subsequent addresses, the scanning
cycle is started again. If the Master recognizes incorrect answers from a slave,
the fault message "Fault RS485" is issued by the Master.
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