Rs-485 Transition Timer Setup; Rs-422 & Rs-485 Termination Resistor - TC Communications TC1540 User Manual

RS-485 Transition Timer Setup

The following table provides setup information for configuring the front panel's DIP switches for an RS-485
application. To use the table, determine the baud rate of your application and set SW6, SW7, & SW8
accordingly. For example, if you know the async data baud rate of your application is 9600, then set SW6
to the Right; SW7 and SW8 to the Left (on each unit). You may also want to try the 25Kbps or 50Kbps settings
for a 9600 baud rate as a test to make sure you have the correct data rate (sometimes the best results come
from trial and error). For RS-232 and RS-422 interfaces, these three switches should be kept in the Left
position.
4-wire
RS-422
x
SW-6
x
SW-7
x
SW-8
RS-422 & RS-485 Termination Resistor
A termination resistor is usually necessary for RS-422 and RS-485 applications. Without proper termination,
the error rate of data transmission may be high due to an "echo" effect on the electrical connection. With
the addition of a termination resistor at the beginning or end of the electrical bus, this echo effect is greatly
reduced. The termination resistors are 100 to 130 ohm resistors located inside the TC1540. Two jumpers,
identified as board locations "W1" & "W5," control the termination resistance on each unit (installed by
default). "W1" controls the resistance for the unit's receiver (IN), while "W5" controls the transmitter's
(OUT) resistance. Proper line termination is required when TC1540 is placed at the end of RS-422/RS-485
bus. There is no termination resistor required for RS-232 applications.
10Kbps 25Kbps
1msec 400 ms
x
x
x
x
x x
When SW6,7,8 are all at left side, the electrical interface is set for RS-422
Table 1. RS-485 Transition Timer Setup Table
remove two screws, then remove the top cover
Note:
Opening the unit without prior consent from
TCCI will result in voiding the warranty.
W1
IN OUT
RS422
SIG
RS485
GND
Figure 7. TC1540's Termination Resistor Locations
50Kbps 100Kbps 250Kbps
200 ms 100 ms 40 ms
x x
x x
x
x
x
W5
10-14VDC
18-36VDC
36-72VDC
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TC1540D User's Manual
500Kbps
1Mbps
20 ms 4 ms
x
x x
x x
x x x
Rev. 1.2