Michael Farrugia

VDDA on MC9S12XDP512

Discussion created by Michael Farrugia on Sep 29, 2006
Latest reply on Oct 4, 2006 by bigmac
I am using the MC9S12XDP512.
VDDR is connected to a 3.3Volts voltage regulator.
I hoped to connect the VDDA to 5Volts so as to be able to connect to external devices which use 5Volts analog signals.
However when I connect the 5Volts supply to the VDDA and VRH inputs the VDDR becomes some 4V!
Is it not allowed to connect the VDDA to a voltage which is higher than VDDR?
I have searched all over in the datasheets and cannot see anything which states this.
What is also interesting is that if I leave these pins (VDDA and VRH) unconnected there is a voltave of about 2.68Volts on these pins.
Can someone explain this behavour please?  I am sure that I am missing something
Thanks a lot