Bms Protocol - Bender ISOMETER isoPV1685RTU Manual

Device communication
Correct arrangement
Three examples for correct arrangement:
Wrong arrangement
Three examples for wrong arrangement:
Wiring
The following cable is recommended for wiring the RS-485 network:
Shielded cable, core diameter 0.8 mm (e.g. J-Y(St)Y 2x0.8), shield connected to earth (PE) on
one end.
The max number of bus nodes is restricted to 32 devices. If more devices are to be connec-
ted, Bender recommends the use of a DI1 repeater.
8.1.2

BMS protocol

This protocol is an essential part of the Bender measuring device interface (BMS bus proto-
col). 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. Only one master may
exist in each network. All bus devices are identified by a unique BMS address. The master
cyclically scans all other slaves on the bus, waits for their response and then carries out the
corresponding commands.
A device receives the master function by assigning bus address 1 to it.
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