GPIO power on STM32 (STM32F205RBT6) can be different voltages?

[woolfson]

Posted on June 07, 2013 at 18:47

Good morning. First time poster.  I am somewhat new at using the STM32 line of MCU's and have a general question that nobody can seem to answer for me.  I am using the STM32F205RBT6 inside of a design.  The STM32 will talk to a couple of different parts; one of the parts uses 1.8v for its' I/O , the other part uses 2.4v for its' I/O.  

If I power the MCU with 3.3volt, does the GPIO output at 3.3volt; if I power the MCU at 1.8v, does the GPIO output at 1.8v?  Is there any way to power the MCU with 3.3v but bias the GPIO at 3.3v; or visa-versa?  Without using something like a Texas Instruments  SN74AVC4T245 bus level shifter?

Thank you, in advance, for your thoughts.

[Tesla DeLorean]

Posted on June 07, 2013 at 19:05

The core runs at ~1.25V, the supply you place externally 2.8V, 3.0V, 3.3V or whatever will be the voltage used for the GPIO VCC ring. As far as I'm aware there is a single ring, and different GPIO banks cannot use different supplies.

If you place higher voltages on pins *not* designated as FT (Five Volt Tolerant) this will feed onto the ring. Most pins are FT, but check the data sheet/manual.

You could run the chip at a lower voltage, have inputs tolerating higher voltages, and outputting higher voltages by using OD mode, and pull-ups to the higher voltage.

You'd still need to check the VIL/VIH and VOL/VOH requirements on either end.