20
W&T
Universal Fiber Optic Interface Converter
RS485 4 wire / RS485 2-wire application with echo
One data channel in each direction is available. The RS485
output driver is activated automatically with each transmis-
sion of data, and goes to the high impedance state again
after the end of transmission. The RS485 receiving channel is
always active in this operating mode.
RS485 2 wire application without echo
One data channel in each direction is available. The RS485
output driver is activated automatically with each transmis-
sion of data, and goes to the high impedance state again
after the end of transmission. The RS485 receiving channel is
deactivated when the driver is on, but is switched on when
the driver is in the high impedance state.
Please see the following table for an explanation of the
operating mode DIP switch:
Operating mode
SW1
SW2
SW3
SW4
SW5
SW8
RS232
OFF
OFF
OFF
OFF
OFF
ON
RS422, RS485, 4-wire bus-master
OFF
OFF
OFF
ON
OFF
OFF
RS485, 4-wire/2-wire with echo
OFF
ON
OFF
ON
OFF
OFF
RS485, 2-wire without echo
ON
ON
OFF
ON
OFF
OFF
Termination
For all RS485 operating modes it is essential that the bus
system be terminated with a termination network which
assures a defined rest state in the high-impedance phases
of bus operation. The bus system can be connected to a
termination network by closing switches #6 and #7 on the
interface module:
