Texas Instruments RS-485 Half-Duplex Evaluation Module RS485-HF-DPLX-EVM RS485-HF-DPLX-EVM Datenbogen
Produktcode
RS485-HF-DPLX-EVM
Vcc
GND
B
A
D
R
1
2
4
5
6
7
8
DE
3
U1
RE
DUT_VCC
R5
120 W
0V
3.3V
Receive
Data
B
A
Transmit
Data
V
OD
0W
R8
0W
R9
B
A
V
A
V
B
Powering Up the EVM and Taking Measurements
3
Powering Up the EVM and Taking Measurements
The generally recommended procedure for taking measurements is listed:
1. Install the required ground connections.
2. Connect the oscilloscope with the respective probe points you want to measure.
3. Adjust the power-supply to match the V
CC
requirements of the selected RS-485 device.
4. Adjust the generator outputs for a maximum output signal level, based on the V
CC
requirements of your
selected RS-485 device, or check the logic switching levels of the controller I/O.
5. Connect the power supply conductor with pin 3 of TB1 and observe the blue LED (D1) turning on.
6. Connect signal conductors from the controller or the generator with their corresponding EVM inputs at
JMP2 to JMP4.
7. Logic high at the receiver output, R, will turn on the red LED (D3), and logic high at the driver input, D,
turns on the green LED (D2). If D is left open, an internal 100-k
Ω
pull-up resistor provides logic high
instead. However, due to the small input current, D2 will remain off.
3.1
Measurement Examples
Each of the following measurement examples show the equivalent circuit diagram and the corresponding
EVM setup. Only the measurement relevant headers and terminal blocks are shown, and not necessarily
at their exact location on the EVM.
EVM setup. Only the measurement relevant headers and terminal blocks are shown, and not necessarily
at their exact location on the EVM.
1. Standard Transceiver Configuration
Normal transceiver operation requires both the driver and the receiver sections being active. Therefore,
the receiver enable pin (RE) must be at logic low potential and the driver enable pin (DE) at logic high.
the receiver enable pin (RE) must be at logic low potential and the driver enable pin (DE) at logic high.
Transmit data entering at the D-input terminal appear as the differential output voltage (V
OD
= V
A
– V
B
)
on the bus wires, A and B. Via the active receiver, it is possible to sense the data traffic in transmit
direction.
direction.
Figure 5. Transceiver Configuration for Normal Operation
shows the corresponding EVM setup. EARTH and GND 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),
in this example, is connected to the 3.3-V output of a power-supply unit (PSU).
in this example, is connected to the 3.3-V output of a power-supply unit (PSU).
5
SLLU173B – October 2012 – Revised June 2013
RS-485 Half-Duplex Evaluation Module
Copyright © 2012–2013, Texas Instruments Incorporated