Cactus

Output voltage on pins

Recommended Posts

What is the output voltage level for 'high' signals on the Papilio Pro? I'd like to communicate with 3.3V components from it, is that possible by just connecting directly to the pins?

I see there are separate 3.3V and 5V power pins. If I have a component that requires 3.3V signals and another that requires 5V, is there a way to communicate with both with a single Papilio Pro?

Share this post


Link to post
Share on other sites

Hi Cactus,

according the the Spartan 6 Family Overview (http://www.xilinx.com/support/documentation/data_sheets/ds160.pdf) the chip is compatible with several low voltage families from 3.3V down to 1.2V. From the Papilio Pro schematic it looks like all 4 IO banks are supplied from the 3.3V rail. So i'd say ok to connect with 3.3V logic, do not connect to 5V logic.

 

More information on the IO capabilities here:

http://www.xilinx.com/support/documentation/user_guides/ug381.pdf

 

Cheers,

Steve

  • Like 1

Share this post


Link to post
Share on other sites

Hello Cactus,

 

All I/O on the Papilio Pro is 3.3V. You can connect to any 3.3V component with no problem. To communicate with a 5V part you need to put a 390 ohm resistor in between the Papilio I/O pin and the pins on the component you are connecting to. This will protect the 3.3V pin on the Papilio from too much current.

 

Jack.

Share this post


Link to post
Share on other sites

Thanks, that's very helpful. And what if I need to do output to a 5V device? I guess I could use one transistor per line, but is there an easier way?

Share this post


Link to post
Share on other sites

Hello Cactus,

 

It depends what you mean by output. If you are driving 5V TTL logic then the 3.3V that is output by the Papilio is high enough to be considered a High signal. Please take a look at this:

https://learn.sparkfun.com/tutorials/logic-levels/ttl-logic-levels

You can see that 2V is considered a High logic level, so the 3.3V output by the Papilio will drive a 5V device just fine. 

 

Usually you only need to provide 5V for power which you can draw from the 5V pin on the Wing header. I have yet to run into a 5V device that needed anything more then that. RAMPS is the only thing I've heard of that is the exception and I've never really looked to closely to understand why....

 

Jack.

Share this post


Link to post
Share on other sites

Actually, the logic detection level will depend on a large number of factors. If you have a stable (i.e., resistive) design, 3.3V should work just fine. If you have high inductive/capacitive paths, then you may have a problem.

If you can test a direct drive, and if it works, excellent. Otherwise you can get some level shifters, but they can be expensive ($2 for a 8-line), and you will need to take care of bidirectionality yourself - the "automatic" ones seldom work.

 

Alvie

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now