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Receive
data
0V
5V
Transmit
data
Figure 6
shows the corresponding EVM set-up. Earth and ground receive the same reference potential,
PSU-ground, through the wire-bridge from pin 1 to pin 2 at the terminal block, TB1, while pin 3 (VCC)
is connected to the 5 V output of a power-supply unit (PSU).
The low potential for RE is provided by the wire-bridge from pin 2 to pin 3 at JMP2, and the high
potential for DE through a wire-bridge from pin 2 to pin 1 at JMP3. Data from the signal generator enter
the board at pin 2 and pin 3 of JMP4. This data is measured via channel 1, which is connected to pin 1
and pin 2 of JMP14. Channel 2 measures the receive data at JMP11, and channels 3 and 4 the bus
voltages, V
and V
A
2. Operation Under Maximum Load
EIA-485 (RS-485) specifies three maximum load parameters: a maximum differential load of 60 Ω, a
maximum common-mode load of 375 Ω for each bus wire, and a receiver common-mode voltage
range from –7 V to +12 V.
under maximum load conditions the transceiver must be capable of sourcing and sinking bus currents
of up to 55 mA. The purpose of this test is to show the robustness of V
common-mode voltage range at maximum load.
SLLU128A – June 2010 – Revised August 2010
U1
R
1
RE
2
DE
3
D
4
Figure 5. Transceiver Configuration for Normal Operation
Signal
Generator
5V
JMP2
1
VCC
2
/RE
3
4
JMP3
1
VCC
2
DE
3
4
JMP4
1
VCC
2
3
4
Figure 6. EVM Set-up for Normal Transceiver Operation
, at JMP6.
B
Figure 7
reflects these requirements through R5, R8, R9, and V
Copyright © 2010, Texas Instruments Incorporated
Powering up the EVM and Taking Measurements
DUT_VCC
Vcc
8
B
7
R5
A
120 W
6
GND
5
V
B
Scope
PSU1
Ch1
Ch2
Ch3
Ch4
TB1
JMP11
1
R
2
3
JMP6
1
HVD96
2
B
EVM
3
A
4
JMP14
1
D
2
3
OD
R8
B
B
0W
V
OD
R9
A
A
0W
V
A
5V
. Note that
CM
over the entire
Sympol™ Transceiver
5
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