Texas Instruments RS485-HF-DPLX-EVM, User Manual, Page: 6 / 14

PSU1
V
CM
PSU2
Scope
Ch4 Ch3 Ch2 Ch1
3.3V
Signal
Generator
JMP4
1
2
VCC
3
4
R
D
JMP3
1
2
VCC
3
4
JMP2
1
2
VCC
3
4
/RE
DE
JMP6
1
2
3
4
1
JMP11
2
3
1
JMP14
2
3
1 2 3
TB1
G
N
D
E
A
R
T
H
V
C
C
JMP7
1
2
3
4
R9
375 W
R8
375 W
3.3V
Vcc
GND
B
A
D
R
1
2
4 5
6
7
8
DE
3
U1
RE
DUT_VCC
R5
60
W
0V
3.3V
Receive
Data
B
A
Transmit
Data
V
OD
375
W
R8
375
W
R9
V
CM
= -7V to +12V
Powering Up the EVM and Taking Measurements
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Figure 6. Configuration for Maximum Loading
While the cable connections of the signal generator and the oscilloscope remain the same as in the
previous example, the following board changes need to be implemented to reflect maximum load
conditions:
• replace R5 (120- Ω default) with 60 Ω
• replace R8 and R9 (0- Ω default) with 375 Ω
• connect pin 2 of JMP7 with pin 1 and pin 3 with pin 4
• replace the previous wire-bridge at TB1 with a second power supply unit (PSU2) and connect the
ground terminals of both, PSU1 and PSU2 with a wire-bridge, as shown in
Figure 7 .
Figure 7. RS-485 Half-Duplex EVM Setup for Maximum Loading
Note that Figure 7 only shows the wiring of PSU2 for positive common-mode voltages. For negative
V
CM
, connect the ground terminal of PSU2 with pin 1 of TB1 (EARTH), and the V
CM
-output of PSU2
with the ground terminal of PSU1.
6 RS-485 Half-Duplex Evaluation Module SLLU173A – October 2012 – Revised November 2012
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