Texas Instruments Sympol SN65HVD96, User Manual

Page: 5 / 12

Vcc
GND
B
A
D
R
1
2
4 5
6
7
8
DE
3
U1
RE
DUT_VCC
R5
120
W
0V
5V
Receive
data
B
A
Transmit
data
V
OD
0 W
R8
0
W
R9
B
A
V
A
V
B
Scope
Ch1 Ch2 Ch3 Ch4
5V
PSU1
5V
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
B
A
1
JMP11
2
3
1
JMP14
2
3
1 2 3
TB1
G
N
D
E
A
R
T
H
V
C
C
HVD96
EVM
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Powering up the EVM and Taking Measurements
Figure 5. Transceiver Configuration for Normal Operation
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).
Figure 6. EVM Set-up for Normal Transceiver Operation
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
A
and V
B
, at JMP6.
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. Figure 7 reflects these requirements through R5, R8, R9, and V
CM
. Note that
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
OD
over the entire
common-mode voltage range at maximum load.
5 SLLU128A – June 2010 – Revised August 2010 Sympol™ Transceiver
Copyright © 2010, Texas Instruments Incorporated