HARDWARE DESCRIPTION
RS485 bus termination and stabilisation
baud rate
RS485 bus termination and stabilisation
TERMINATION
At high transmission rates or long distance, RS485 bus termination is necessary.
The termination on RS485 bus must be set on both ends of the RS485 bus.
STABILISATION
Some device, to work properly, demands that RS485 must always be in known and valid state.
That is, when + (positive) pin is more than 200 mV positive than – (negative) pin. Pins + and –
are sometimes marked as A and B. In case that no device on RS485 bus is transmitting or in
case of short circuit, there is no voltage difference between those pins and some device do not
work correctly.
On this port board so called „true fail-safe“ RS485 chip is used so board works correctly without
stabilisation at invalid RS485 bus state. But still switches for stabilisation are provided on port
board.
The stabilization on RS485 bus may be set on one device only!
Switches at the lower side of connector:
Switch
4
5
6
Description
RS485 stabilisation
RS485 termination
RS485 stabilisation
Switches at the upper side of connector:
BAUD rate
bit/s
Switch
Interface 5
Interface M
Interface L
1
2
3
19200
4800
300
OFF
OFF
OFF
38400
9600
600
OFF
OFF
ON
57600
19200
1200
OFF
ON
OFF
Company:
Device:
Document:
Code:
Date:
Page:
Ediseja 21 CMU 100 / 1.5.S - 0
User manual CMUMU15S
9
Picture 4: RS485 BUS schematic