Serial RX/TX from the Arduino at 5v

I think that is called RS485, but not sure.

I am working on a project and there is a device spitting out 1200 baud (8n1) and it goes to the Arduino.
There it is "looked at" and actioned as needed.

Thing is, I don't know how I can do this and flash the Arduino with new software if it doesn't work while still in situe/place. (spelling?)

I am not exactly sure WHAT is sent. (At 5v signal levels)

So it isn't that I can have the serialmonitor open as well.

I have heard of the beast FTDI, but know nothing of it. Other than it is another way to program the Arduino.

I shall go and try to learn about it too, but was looking for pointers from people who may have been here before.

It is tricky because:
As it is 5v levels, I can't exactly watch the data with a PC. And an Arduino has only one (?) comm port, and so if it is receiving data from the other device, it can't really report back to the PC what it is seeing.

The only "cheat" way around it (kinda) is to read 'n' characters from the END and read them backwards, sort of thing.

That way, any "header" of which I don't know is negated, as the important stuff (the last 8 characters) are ..... the last 8 characters.

Read in the string (?term?) and look at the right-most 8 and use them.


(Oh, I don't get e-mails of responses, so if you reply and it is weeks before I reply to you: It is not that I am being rude. It is just I am not getting the e-mails sent to me.)

I shall try to keep an eye here, but I have about 30 tabs open doing just that with other sites and it gets annoying when I want to go online and quickly look at something and I have to wait while all the other 30 pages load.
(That's on a good day) It has been up to ..... about 80 tabs I think at one stage.



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First of all, do you have more information about that device and the serial communication ?
It is connected to an Arduino ?
That means the RX and TX are TTL 5V levels ?

Saleae ( has logic analyzers with software that decodes the pulses of data, it will also show the serial data.

Do you have an Arduino Leonardo/Micro or Arduino Mega ? Those have a spare hardware serial port.
With an Arduino Mega 2560 you can connect two spare serial inputs to both the RX and TX of that device, and listen to both RX and TX.

It would be best to use an Arduino with an extra HardwareSerial port but if you only have an Uno or Nano you can use SoftwareSerial to create an extra port. That way you leave HardwareSerial free for uploading programs.


Thanks both for the replies.

ULTIMATELY it will be a NANO I think. Small profile.

But for testing I can use an UNO/ELEVEN.

How do I make a software serial port?

That sounds like a better idea as Robin2 said, as it would keep the standard one free for software updates. THOUGH......
Once flashed, I don't think it will get many updates.

RTFM SoftwareSerial