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TC1540D User's Manual
Rev. 1.2
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.
Table 1. RS-485 Transition Timer Setup Table
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.
Figure 7. TC1540's Termination Resistor Locations
When SW6,7,8 are all at left side, the electrical interface is set for RS-422
SW-6
SW-7
SW-8
4-wire
RS-422
400 ms
1msec
10Kbps
25Kbps
50Kbps
100Kbps
250Kbps 500Kbps
1Mbps
200 ms
100 ms
40 ms
20 ms
4 ms
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
W1
W5
OUT
+
IN
+
RS422
RS485
36-72VDC
18-36VDC
10-14VDC
+
SIG
GND
remove two screws, then remove the top cover
Note:
Opening the unit without prior consent from
TCCI will result in voiding the warranty.
