D
David
- Jan 1, 1970
- 0
I am a little confused by the biasing requirements of RS485 bus for Modbus.
I normally bias the RS485 driver with A > B to ensure a HIGH at any
receiver on the bus when now transmission is in progress.
The standard though states that B must be higher than A for idle state
of the RS485 bus. If I bias like this, the micro in the device will
continually think a start bit is being received due to a low on the
RS485 IC (MAX485).
All practical applications I have seen so far bias A > B.
Could someone shed some light on this for me please.
Regards
David
I normally bias the RS485 driver with A > B to ensure a HIGH at any
receiver on the bus when now transmission is in progress.
The standard though states that B must be higher than A for idle state
of the RS485 bus. If I bias like this, the micro in the device will
continually think a start bit is being received due to a low on the
RS485 IC (MAX485).
All practical applications I have seen so far bias A > B.
Could someone shed some light on this for me please.
Regards
David