Communication with FTDI RS485

Hi all, I have purchased a FTDI usb to RS485 converter to talk to my industruino. However I fail to recieve and/or send data from/to the arduino. From what I understand the Serial1 should be connected to the RS485 port? And digital pin 9 should be set to high to enable the RS485 port on the industruino?

Per example from the modbus master and slave example I have removed the 560R jumpers from the industruino (slave) and have attached the 120R wires of the FTDI converter to the A and B channel.

Industruino      FTDI
GND                GND (RS485)
A                      Data+ (A) and 120R pin1
B                      Data- (B) and 120R pin2

Any ideas why I'm not receiving any data would be greatly apreciated!

Modbus master and slave example:


#include <UC1701.h>


#include <Indio.h>

#include <Wire.h>


#define RS485_ENABLE_PIN 9


void setup() 


  Indio.digitalWrite(RS485_ENABLE_PIN, HIGH); 


  Serial1.begin(9600);  //open the TX/RX port



void loop() 


  Serial1.write("Hello world"); 


  if (Serial1.available()) 


    int inByte =;








- Arnoud

| 3 1 2
Asked on 4/22/16, 12:32 PM

Hi Arnoud, the pin 9 on the IND.I/O is the TxEnablePin, which means it has to be HIGH during transmission. In your above sketch, this pin stays HIGH from Setup, so in theory you won't be able to receive anything, which is the opposite of what you are reporting. Can you please double check? This reference may be useful: (it uses software serial but the Industruino can use hardware serial1)

| 1 1 3
Answered on 6/1/16, 8:50 AM

Hi Arnoud, actually i just saw a mistake in the above code, the TxEnablePin is not an Indio pin, but a pin connected directly to the mcu, so you should use it with the standard digitalWrite (not Indio library): digitalWrite(9, HIGH); Hope this helps- Tom

on 6/1/16, 9:04 AM

I have managed to receive data from the USB FTDI device, however I fail to send data from the Arduino. I have checked with my logic analyzer and there is no change on the A or B pin of the RS485 port on the industruino.

How do I enable the send mode on the MAX485?

| 3 1 2
Answered on 5/26/16, 1:47 PM

As far as I know about RS485 chips, D9 should be high when sending and low when receiving, or viceversa. It is not a chip select pin but a direction pin. Check on a RS485 chip datasheet.

Stefano Giuseppe Bonvini
on 6/1/16, 1:13 PM

looking at the example and at the datasheet, RS485 pin 9 is not an Indio pin, but a MCU pin.
So it should be addressed as a normal Arduino pin, I think.

Stefano Giuseppe Bonvini
on 7/8/17, 6:42 PM

Stefano is correct, the RS485 direction pin is a GPIO pin, not a field side IND.I/O pin. So it should be address in the standard Arduino way, digitalWrite NOT indio.digitalWrite.

Loic De Buck
on 7/17/17, 3:40 AM

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Asked: 4/22/16, 12:32 PM
Seen: 5158 times
Last updated: 7/8/17, 7:19 PM