2-CH RS485 HAT

2-CH RS485 HAT 2-CH RS485 HAT for Raspberry Pi

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Primary Attribute Category: Modules, Raspberry Pi {{{userDefinedInfo}}}: {{{userdefinedvalue}}} Brand: Waveshare

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Onboard Interfaces RPi RS485

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Overview

Introduction

This is a dual-channel isolated RS485 expansion board specially designed for Raspberry PI, which adopts SC16IS752+SP3485 solution, embedded with protection circuits such as power supply isolation, ADI magnetical isolation, and TVS diode, etc. It is easy to control the 2-channel RS485 for auto-transceiving via the SPI interface. Due to its fast communication, stability, reliability, and safety, it is an ideal choice for fields like industrial automation.

More

Feature

• Standard Raspberry Pi 40PIN GPIO extension header, supports Raspberry Pi series boards.
• Adopts SC16IS752+SP3485 dual chip combination, converts SPI to RS485, data rate up to 921600bps.
• Allows transceiving data manually or automatically, configured by DIP switch.
• Onboard TVS (Transient Voltage Suppressor), effectively suppresses surge voltage and transient spike voltage in the circuit, lightningproof & anti-electrostatic.
• Onboard resettable fuse and protection diodes, ensure the current/voltage stable outputs, provide over-current/over-voltage proof, and improve the shock-proof performance.
• Onboard LEDs for indicating the power and transceiver status.
• Breakout SPI control pins, for connecting with host control boards like Arduino.
• Comes with online development resources and manuals (examples in C and Python).

Parameter

• UART expansion chip: SC16IS752
• RS485 transceiver: SP3485
• Communication interface: SPI
• Data rate: 300 ~ 921600 bps
• Operating voltage: 3.3V / 5V
• Dimensions: 65mm × 56.5mm
• Mounting hole size: 3.0mm

Interfaces

PIN	SYMBOL	Description
1	VCC	3.3V/5V Power
2	GND	Ground
3	SCLK	SPI Clock input
4	MOSI	SPI Data input
5	MISO	SPI Data output
6	CS	SPI Chip Selection
7	IRQ	Interrupt output
8	EN1	Enable Channel 1 output
9	EN2	Enable Channel 2 output

Working Principle

Introduction

This product adopts SC16IS752 as a controller. SC16IS752 is a dual-channel high-performance UART expansion chip that supports SPI and I2C. This module adopts the SPI interface and onboard power isolation, ADI magnetic coupler isolation. It also onboards TVS (transient voltage suppression tube), self-recovery fuses, protection diodes, and an automatic transceiver switching circuit. It can effectively suppress the surge voltage and transient peak voltage in the circuit, prevent lightning and static electricity, prevent over-voltage, improve the anti-impact ability, and can conduct signal isolation with high dependence, strong anti-interference, and low power consumption advantages, etc.

Communication Protocol

• CS: Slave chip selection, when CS is at a low level, the slave chip is enabled.
• SCLK: SPI communication clock.
• MOSI/SI: SPI communication host sends, the slave receives.
• MOSI/SI: SPI communication host receives, the slave sends.
• Timing Sequence: CPHL=0, CPOL=0 (SPI0).

Working with RPI

How to use

We provide C and Python demo codes for Raspberry Pi. A quick testing example is provided in Python.

Hardware Connection

• Note: For C and Python demo, an additional RS485 TO UART module is required to connect to channel 1 for observing the effect. "test.py" in Python requires the connection between channel 1 and channel 2.

PIN	Raspberry Pi(BCM)	Description
VCC	5V	3.3/5V Power Input
GND	GND	Ground
SCLK	P21 (SPI1 SCLK)	SPI Clock Input
MOSI	P20 (SPI1 MOSI)	SPI Data Input
MISO	P19 (SPI1 MISO)	SPI Data Output
CS	P18 (SPI1 CS)	SPI Chip Select
IRQ	P24	Interrupt Output
EN1	P27	Channel 1 TX/RX enable: high for TX, low for RX
EN2	P22	Channel 2 TX/RX enable: high for TX, low for RX

Software setup

• Open the terminal and modify the config.txt file by commands:

sudo nano /boot/config.txt

• Add the line below to the file, the int_pin should be set according to the actual welding:

dtoverlay=sc16is752-spi1,int_pin=24

• Then restart Raspberry Pi.

sudo reboot

• After rebooting, the driver of SC16IS752 will be loaded into the system kernel. You can run the command ls /dev to check the following devices:

In the Raspberry Pi system on May 27, 2020, gpiochip3 is replaced as gpiochip2.

Install Libraries

• Install wiringpi:

sudo apt-get install wiringpi
# An upgrade may be required for Raspberry Pi 4B:
cd /tmp
wget https://project-downloads.drogon.net/wiringpi-latest.deb
sudo dpkg -i wiringpi-latest.deb
gpio -v
# Running gpio-v to check if the version is 2.52, If it is not, you need to check the installation again.

• Install the python2 library:

sudo apt-get update
sudo apt-get install python-pip
sudo pip install RPi.GPIO
sudo apt-get install python-serial

• Install the python3 library:

sudo apt-get update
sudo apt-get install python3-pip
sudo pip3 install RPi.GPIO
sudo apt-get install python3-serial

Test

• Download and run the examples:

sudo apt-get install p7zip-full
wget https://files.waveshare.com/upload/4/44/2-CH_RS485_HAT_code.7z
7z x 2-CH_RS485_HAT_code.7z
sudo chmod 777 -R  2-CH_RS485_HAT
cd 2-CH_RS485_HAT/

• You can also clone the project from our GitHub:

sudo git clone https://github.com/waveshare/2-CH-RS485-HAT
cd 2-CH-RS485-HAT/

• Note: the directory of the example demo should be based on the actual one.
• C demo:

cd c
make clean
make
sudo ./main

• Python demo:

cd python 
cd examples
sudo python main.py
#Or
sudo python3 test.py

Hardware connection: Channel 1 of the 2-CH RS485 HAT is connected to USB TO RS232/485/TTL:

Connect USB TO RS232/485/TTL to the computer, open the serial port assistant software, select the corresponding serial port, and set the baud rate to 115200.

• Run the C program, the data sent by computer will all be received by Raspberry Pi, as below:
  

Note: Line breaks need to be added for data to be returned. Otherwise, the data won't be returned. The directory of the example program should be based on the actual one.

• Run the main.py, the data sent by the computer will all be received by Raspberry Pi, as below:

Note: Line breaks need to be added for data to be returned. Otherwise, the data won't be returned. The directory of the example program should be based on the actual one.

If there is no other RS485 device, you can choose the following test method to connect A,B of channel 1 to A,B of channel 2:

• Running result of test.py:
  

Resources

Documentation

• Schematic
• 3D Drawings

Demo code

• Demo code
• Github

Datasheets

• SP3481/SP3485 User Manual
• SC16IS752 Datasheet

FAQ

Question:485 speed is too high to communicate?

 Answer:

If the automatic transceiver is used, you will find that it can only reach 921600 bps at most, and the manual transceiver can reach 2M when testing.

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Question:In the semi-automatic mode (manual mode), the green RXD light or the green TXD light is always on?

 Answer:

In the semi-automatic mode, the voltage on the EN pin determines whether RS485 is transmitted or received. In the transmit mode, the RXD green light may be always on. In the receive mode, the TXD green light may be always on, which is normal.

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Question:485 communication is abnormal, what should I do?

 Answer:

1. Check whether A and B of 485 correspond to the controlled devices.
2. You can use the USB to 485 device to communicate with the module first to ensure that there is no problem with the settings of the Raspberry Pi;
3. Check the setting of odd and even bit parity of serial communication parameters.

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Question:Can the Ubuntu system be installed on the Raspberry Pi? Why can't I find the config.txt file in the boot folder?

 Answer:

1. The Raspberry Pi is installed with the mainstream Ubuntu system and can be used.
2. Ubuntu's config.txt file is usually in the /boot/firmware folder.
3. You also can use the SD card of the Raspberry Pi to read and change the config.txt file under the computer (or other hosts that can recognize the SD card) through a card reader.

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Question:Is it possible to use Ubuntu on a Raspberry Pi, and why can't I find the config.txt file in the boot folder?

 Answer:

1. Raspberry Pi is installed with the mainstream Ubuntu system.
2. The config.txt file for Ubuntu is usually located in the /boot/firmware folder.
3. The Raspberry Pi version of the Ubuntu system is generally 64-bit, and you can install the WiringPi library using the following command.

Download 64-bit Arm wiringpi
wget https://gitee.com/LJYSCIENTIST/raspberry-pi-software-storage/raw/master/wiringpi-2.60-1_arm64.deb 
Install 64-bit Arm wiringpi
sudo dpkg -i wiringpi-2.60-1_arm64.deb 

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Question:Why can't the corresponding demo receive the data after connecting the sensor to the RS485?

 Answer:

The data sent from the sensor may be in Hex format (sometimes you need to send the data in hex to the sensor to request the data). Please transmit and receive the HEX data according to the following steps:

wget https://files.waveshare.com/upload/0/01/RS485-CAN-HAT-For-Hex.zip
unzip RS485-CAN-HAT-For-Hex.zip 
sudo chmod 777 RS485-CAN-HAT-For-Hex.zip
cd RS485-CAN-HAT-For-Hex
sudo python3 RS485-CAN-HAT-send-hex.py  

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Question:Can I use 2-CH RS232 HAT and 2-CH RS485 HAT simultaneously?

 Answer:

I'm sorry that does not support.

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Question:What are the 120Ω terminal resistor switch used for?

 Answer:

The 2-CH RS485 HAT with a 120-ohm resistor is used for termination in RS485 communication networks to reduce signal reflections and improve signal integrity.

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Support

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