Generation of RS422/485 signal using portenta H7

Hello evryone,
I need to generate a RS422/485 signal using the portenta H7, I need to add the printed board max490 to ensure the RS422/485 communication.
So my question is : how could I generate this signal and how should I connect rhe printed board (max490) with the arduino board portenta

this is the datasheet of the printed board max490 : MAX481 DS (

Datasheet of portenta H7; Pinout-PortentaH7_latest.pdf (


No, wrong choice. The MAX490 is a 5V device, so if you want to use this chip you need a level converter between it and the Potenta.

You only supplied a link to the chip, not to the circuit board. I guess you don't connect the chip directly.

Provide much more information about your project. What other device do you want to connect to?

Do you need full-duplex RS-485 (as the MAX490 provides)?

hello pylon,
thank you for your response.
actually I need to generate a signal RS422/485 via the PORTENTA H7 to communicate with an aéronautic device who use the RS422/485 protocole to communicate ( normally we need just half-duplex).
the aim of the project is to make a diagnostic and localise the failure in the device with a looping test (looping the signals of the device in/out ) so here I need to make the portenta generate, transmite and recieve a RS422/485 signal

for the max490 I didn't understand why should I use a level converter the portenta h7 provide the 5V !!

The portenta may be able to provide the max chip with 5V power, but the portenta's data pins are 3.3V and will be damaged if connected directly to a chip outputting 5V signals.

@thalesmaissa, your topic has been moved to a more suitable location on the forum.

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hello PaulRB,
thank you for your response. I get it. so I need to use a level converter in the pins TX and RX of the portenta before connecting them to the max chip ?
as chowen here

should I get the modbus RS485 to ensure the communication or I can keep the max490 and use a level converter ( or 2 resistences) ?
thank you .

Tx from the portenta should be ok to connect directly to the Rx on the max490. The max490 should recognise 3.3V as HIGH.

But for Tx from the max490 to Rx on the portenta, you will need a voltage divider to reduce the 5V signal to 3.3V. 10K and 22K should be ok.

Not sure what you mean by "modbus rs485" but if that is actually a max485, then the same applies.

ARCELI 5PCS 5V MAX485 / RS485 Module TTL to RS-485 MCU Development Board: High-tech

RS422 RX TX TTL FULL DUPLEX Convertitore Modulo max490 Arduino esp8266 esp32 STM - Arduiner - Arduino Components Shop

these are the modbus rs 485 and modbuss rs422 witch both use the chips max485 and max 490. I don't know what is the difference between using the modbus and the using just the chip max490!

There is no schematic on either link, so I do not know either.

I can use just the chips max422 and max485.
so for the connection of the different pins of the chip max422 could you please confirm my connexion ......I didn't understand where to connect the 2 resistances to reduce the voltage

See reply #8

there is no TX from the max490 to the the portenta there are only 2 pins TX(portenta )--> DI(MAX490) and RX(portenta) --> RO(MAX490) .
The TX and the RX of the chip MAX490 are connected with the device. as shown in replay#11

thank you

There is only 1 output, which is 5V, from the max chip connected to an input of the portenta which is 3.3V.

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ok, I get it thank you. it was helpful .

thank you for evryone.

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