RE: ground loops or some other strangeness

The I/O is probably 3.3v which is why the supply is regulated to 3.3v.  Everything is going to 3.3v and even lower!  Plan for it.

Some processors have SOME 5V tolerant I/O, but I don't know about this one.

You CAN use 5V logic, but you must take precautions to buffer the I/O so you are not presenting 5V to the I/O.  If you have just a few, you can use transistors to do the buffering, or even a resistor divider.  If you have an entire bus full you can use a level converter chip that takes the two voltages and does the buffering.

Also, DO NOT have the 5V on with the processor voltage off.  That can cause backfeeding and, depending on the chip, can cause damage.  Either turn them on and off together or turn the processor on first and off last.

-Pete F
________________________________
From: [email protected] [mailto:[email protected]] On Behalf Of Luiz Iniciante
Sent: Tuesday, November 12, 2013 9:14 PM
To: [email protected]
Subject: Re: [rabbit-semi] ground loops or some other strangeness



Thanks for the quick answer. But if it is not 5V, what voltage do the rabbit I/Os take?

Regards,
                   L


Em Terça-feira, 12 de Novembro de 2013 23:28, Steve Trigero <[email protected]> escreveu:

I don't believe the RCM6700 is 5V tolerant. You need to be careful not to connect
any rabbit I/O to 5V logic.

Steve


On Monday, November 11, 2013 5:34 PM, Luiz Iniciante <cavaleiro_21-/[email protected]> wrote:

Hello Forum,
                       Thanks for the help so far.
                        I have an additiional problem with the ground of my development board. The RCM6700 development board has a 3.3V rail which I do not find very useful since most components (logic gates, amplifiers etc) operate on 5V. I therefore have separate 5V supply (from a battery) to power the components of my circuit, however I have placed connected the ground of the power supply and that of all components to the same ground of the board.
                         When the board is powered off, the correct voltages appear across all the components. However, when the board is on it is as if the ground is floating above 0V and I no longer have 5V from my battery power supply. Furthermore, if I turn off the the board, I notice that an LED stays weakly lit as if the RCM6700 chip is draining power from the 5V battery supply.
                         Does anyone have any idea what is going on and how it can be fixed?

Regards,
              L