Specifications

RS-422/485 Application Note 35
 Copyright B&B Electronics -- Revised October 1997
B&B Electronics -- PO Box 1040 -- Ottawa, IL 61350
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Multi-Master RS-485 Systems
Each node in a multi-master type RS-485 system can initiate its own
transmission creating the potential for data collisions. This type system requires
the designer to implement a more sophisticated method of error detection,
including methods such as line contention detection, acknowledgement of
transmissions and a system for resending corrupted data.
Systems with Port Powered Converters
RS-232 to RS-422 or RS-485 converters that derive their power from the
RS-232 port are becoming more common in data systems. A good programming
practice is to set unused handshake outputs to a high voltage state in systems
using any type of RS-232 to RS-422 or RS-485 converter. This will assure the
best possible operating conditions for all converters used.