2-CH RS485 HAT

Introduction

This is a dual-channel isolated RS485 extension board specially designed for raspberry PI, which adopts SC16IS752+SP3485 solution, embed 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 SPI interface. Due to its fast communication, stability, reliability, and safety, it is an ideal choice for fields like industrial automation. Template:Amazon

Interfaces

VCC	3.3V
PIN	Description
VCC	3.3V/5V Power
GND	Ground
SCLK	SPI Clock input
MOSI	SPI Data input
MISO	SPI Data output
CS	SPI Chip Selection
IRQ	Interrupt output (Interrupt Request)
EN1	Channel 1 output enable
EN2	Channel 2 output enable

Working principle

Introduction

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This product adopts SC16IS752 as controller. SC16IS752 is a dual-channel high-performance UART expansion chip that supports SPI and I2C interfaces communication. This module uses SPI interface. Onboard power isolation, ADI magnetic coupler isolation, onboard TVS (transient voltage suppression tube), self-recovery fuses, protection diodes, and 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, can conduct signal isolation, with high dependence, strong anti-interference, low power consumption advantages, etc.

Communication protocol

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

How to use

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

Hardware Connection

To run examples, you should prepare an external RS485 to UART module, connect it to Channel 1 of 2-CH RS485 HAT. If you test the 2-CH RS485 HAT with the text.py example, you need to wire Channel 1 and Channel 2 of 2-CH RS485 HAT.

485 PIN	Raspberry Pi(BCM)
VCC	5V
GND	GND
SCK	P21 (SPI1 SCLK)
MOSI	P20 (SPI1 MOSI)
MISO	P19 (SPI1 MISO)
CS	P18 (SPI1 CS)
IRQ	P24
EN1	P27
EN2	P22

Software setup

• Open the terminal and modify 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 command ls /dev to check the following devices:

Install Libraries

• Install wiringpi

sudo apt-get install wiringpi

1. 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

1. 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 http://www.waveshare.net/w/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/

• C program

cd c make clean make sudo ./main

• Python program

cd python cd examples sudo python main.py Hardware connection: Channel 1 of the 2-CH RS485 HAT is connected to the USB TO USB TO RS232/485/TTL: 800px Connect USB TO 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:

800px Note: The path of the samples is based on the actual directory;

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

800px Note: The path of the samples is based on the actual directory; If you don't have other RS485 devices, you can choose the test method as follow by connecting channel 1 with channel 2: 800px

• Running result of test.py :

800px

Resources

Documentation

• Schematic

Demo code

• Demo code
• Github

Datasheets

• SP3481_SP3485.pdf
• SC16IS752_datasheet.pdf

FAQ

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.

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

Answer: 1). Check if the serial communication of the Raspberry Pi has enabled flow control; 2). Determine whether A and B of 485 correspond one-to-one with the controlled 485 devices A and B; 3). You can use USB to 485 module to communicate with 2-CH RS485 HAT to ensure that there is no problem with the Raspberry Pi settings.

Supports

Contact us Working hours: 09:00-18:00 (UTC+8 Monday to Saturday)