TTL to RS422 Module

MAX490 TTL to RS422 Signal Converter Communication Module

Bidirectional 1000 Meters 2.5Mbps DC 5V Full Duplex

     This module converts the TTL UART (serial port) output of a microcontroller to an RS422 line, allowing a TTL device to be connected to an RS422 network over a long cable. The board uses the MAX490E IC (the 15KV ESD protected version of the MAX490 family). The IC has one transmitter and one receiver channel; with this single chip, bidirectional (full duplex) communication is done where data can be sent and received at the same time. Since sending and receiving use separate line pairs, no direction control (DE/RE) pin is needed.

     MAX490 supports communication speeds up to 2.5Mbps; the differential RS422 line is little affected by noise and provides a communication distance of up to 1000 meters (the usable speed drops as the distance increases). It works with a DC 5V supply. The TTL side has a 4-pin male header (VCC / GND / RXD / TXD) and the RS422 side has a 4-pin screw terminal (A / B / Z / Y). The line pins of the IC are 15KV ESD protected; additional TVS protection diodes on the line side, 120ohm termination resistors that reduce reflections on long lines and power / communication indicator LEDs are mounted on the board.

Key features:

     Send and receive at the same time: Thanks to the separate transmitter (Y / Z) and receiver (A / B) of the MAX490 IC, data flows in both directions at the same time over a 4-wire connection; no direction pin or direction control in software is needed.

     Long distance: Communication up to 1000 meters is possible with the differential RS422 line; on short lines speeds up to 2.5Mbps can be reached.

     Line protection: The line pins of the MAX490E IC are 15KV ESD protected; the 4 TVS diodes and series protection resistors on the RS422 line side give additional protection against voltage spikes.

     Ready termination: The 2 on-board 120ohm termination resistors reduce reflection (echo) noise on long lines.

     Easy connection: The TTL side connects to jumper wires with a 4-pin male header and the RS422 side connects to the line cable with a screw terminal, without soldering; power and communication are shown by 3 indicator LEDs.

Features:

• Product type: TTL - RS422 bidirectional signal converter module
• IC: MAX490E (MAX490 family, 1 transmitter + 1 receiver)
• Communication format: RS422, 4 wire, full duplex (bidirectional, simultaneous)
• Communication speed: up to 2.5Mbps
• Communication distance: up to 1000 meters (speed drops as distance increases)
• Operating voltage: DC 5V (MAX490 supply range 4.75V - 5.25V)
• TTL level: 5V logic level
• TTL connection: 4-pin 90 degree male header, VCC / GND / RXD / TXD
• RS422 connection: 4-pin screw terminal, A / B / Z / Y
• ESD protection: 15KV (MAX490E line pins), plus 4 TVS protection diodes
• Protection resistors: series current limiting resistors on the line inputs
• Termination: 2 pcs 120ohm termination resistors, reduce long-distance echo noise
• Indicator LEDs: 3 pcs, power and communication
• Mounting: mounting hole in 4 corners
• Color: Blue PCB, green terminal
• Dimensions: 5cm x 2.7cm
• Weight: approx. 9gr

Usage information:

• On the TTL side, connect VCC to 5V and GND to the microcontroller GND. Connect the TXD and RXD pins to the UART pins of the microcontroller; if there is no communication, swap the TXD and RXD connections and try again.
• On the RS422 side, connect the Y / Z (transmitter) pins of this module to the A / B (receiver) pins of the other device, and the A / B (receiver) pins of this module to the Y / Z (transmitter) pins of the other device. Use twisted-pair cable for each pair.
• On long lines, also joining the GND of both devices with a separate wire makes the communication more stable.
• Choose the speed according to the cable length: high speed on short lines, a low baud rate on lines of hundreds of meters.

Areas of use:

•  Serial communication with PLC and industrial automation devices
•  Sensor and measuring device data acquisition over long distances
•  Weighing scale indicators read over their RS422 output
•  Camera control lines and moving (pan tilt) camera mechanisms
•  SSI interface (clock + data line) absolute encoder and position reader connections
•  Long-distance serial port link between a microcontroller and a computer
•  Long-cable device communication inside buildings and plants
•  Motor drivers and control boards with RS422 communication
•  Extending a TTL UART line in noisy environments

Precautions:

•  The module works with 5V and its TTL output is at 5V level. Use a level shifter if it will be connected to the RX pin of a board running at 3.3V.
•  This module is for RS422 (4 wire, full duplex). It cannot be used directly on 2-wire RS485 lines because it has no direction control.
•  The module has a single transmitter and a single receiver channel. An incremental RS422 encoder with A / B / Z outputs needs a separate receiver for each channel; this module alone is not enough.
•  1000 meters is the maximum distance; 2.5Mbps cannot be used at this distance. Choose a low speed on a long line.
•  The termination resistors are fixed on the board. If more than one receiver is connected to the same line, only the device at the far end of the line should have termination.
•  Make the terminal connections with the power off; do not short the Y / Z transmitter pins to each other or to the supply.

Package contents:

•  1 Piece TTL to RS422 MAX490 Module
•  1 Piece 4-pin 90 degree male header ( Assembled )
•  1 Piece 4-pin screw terminal ( Assembled )
•  Note: Connection cables are not included in the package.