Author Topic: Voltage between Serial Rx & Gnd  (Read 2374 times)

0 Members and 1 Guest are viewing this topic.

Offline @rtTopic starter

  • Super Contributor
  • ***
  • Posts: 1051
Voltage between Serial Rx & Gnd
« on: November 20, 2016, 12:00:05 pm »
Hi Guys :)
I have a pair of Commodore Amiga CD32 retro consoles, So that makes me cool right there :D

I noticed tonight making a serial cable (for receive only) to debug a microcontroller project,
there is voltage between the serial Rx pin and Ground pin whether the serial port is open in software or not.
The port does work as expected, but the Rx pin can light an LED quite well via a 470R current limiting resistor.
Then I tried my other identical console and it was the same!

Does anyone have an explanation for this? I have to have the pins correct because data is received on the Rx pin fine.
The console can run the normal OS like other Amigas, and I use terminal software often for debugging micro projects.
It’s a 5 Volt port, not RS232, or any negative  levels. Transmit from the console is simply on & off.
Cheers :)

EDIT,,, There’d be a better section for this, but I couldn’t delete it myself.

Edit again,,,
Maybe it should be moved to the beginner section.
Hmm, why would you want to normally hold a pin high to stop it floating low and getting noise on it... :D

« Last Edit: November 20, 2016, 12:34:02 pm by @rt »
 

Online PA0PBZ

  • Super Contributor
  • ***
  • Posts: 5121
  • Country: nl
Re: Voltage between Serial Rx & Gnd
« Reply #1 on: November 20, 2016, 01:21:14 pm »
I was just going to post this but you won  :)

Keyboard error: Press F1 to continue.
 
The following users thanked this post: @rt

Offline @rtTopic starter

  • Super Contributor
  • ***
  • Posts: 1051
Re: Voltage between Serial Rx & Gnd
« Reply #2 on: November 20, 2016, 01:34:30 pm »
Lol :)  Thanks! It is slightly less embarrassing to have found it myself :D
I wanted to serial debug a 3.3V micro program, but the tx pin on the microcontroller is not 5 Volt tolerant :O
Maybe it matters less if the pin on the micro is always an output. I guess a series diode will be good enough.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf