How many parallel slave serial/rx inputs can a single master serial/tx support?

I plan on having a master Arduino Due communicate to many slave Arduino Unos (or Micros) through serial. I know current gets divided for each additional slave, but i'm not sure the current that the tx pin puts out, nor do i know the lowest amount of current needed for serial data to be read.

I do not need communication from the slaves back to the master, this is all unidirectional. I also am not considering I2C currently, just want to test the limits of serial right now.

Thank you.

The DUE is a 3.3v board and the Unos are 5v boards. That may make a difference.

You could always feed the signal through an external buffer chip to boost it - something like a 74HC08. With suitable buffering you could communicate with a very large number of slaves.

...R

GregFinger:
I plan on having a master Arduino Due communicate to many slave Arduino Unos (or Micros) through serial

A DUE can output a maximum total current of 800 mA, and I don't think there is any issue using at the same time Serial, Serial1, Serial2, Serial3 and Serial4.

Edit: See max output current pin by pin:
https://www.arduino.cc/en/Hacking/PinMappingSAM3X

As you have many slaves I guess the cables get longer. With a TTL UART signal longer distances are hard to bridge so you might have a look at a technology made explicitly for that: RS-485.

ard_newbie:
A DUE can output a maximum total current of 800 mA, and I don't think there is any issue using at the same time Serial, Serial1, Serial2, Serial3 and Serial4.

Except that the DUE doesn't HAVE a Serial4.

The DUE has a Serial4 ( but yes, you have to add 3 lines of code ).

ard_newbie:
A DUE can output a maximum total current of 800 mA,

NOT on a single I/O pin - which is what the question is about.

...R

OP is assuming that a certain amount of current is pushed each time a bit is transmitted. That is NOT the case. The pin goes high or low, allowing, or not, current to flow. How much actually flows depends on the current demand of the things that are connected to the pin.

There is a documented limit regarding how much current the pin should be allowed to deliver. OP should be intimately familiar with the datasheet, considering his/her project.

Now, the real question might be "How much current does the Uno/Micro/Nano/Ugly Duckling consume, when receiving serial data"? But, that is not what OP asked.

Robin2:
You could always feed the signal through an external buffer chip to boost it - something like a 74HC08. With suitable buffering you could communicate with a very large number of slaves.

Where would you recommend reading about this part? I'm not familiar with it.

PaulS:
"How much current does the Uno/Micro/Nano/Ugly Duckling consume, when receiving serial data"?

yes, this is a more direct question than how i phrased it, and i'd like to get solved. I know the Due can provide 15 mA on each digital pin (and as Robin2 mentioned Due may not be the most appropriate board for this project, so i looked up the Mega and it said provides 20mA on each).

GregFinger:
Where would you recommend reading about this part? I’m not familiar with it.

Google 74HC08 datasheet or just 74HC08

…R