Toggling GPIO Pins very quickly

Hey everyone, I'm working with an MSP430f2012 chip and am tryign to
generate a delta sigma bitstream using a gpio pin. Unfortunatly whenever I
try to toggle the pin at a rate faster than 10kHz, the pin appears to not
be able to fully rise or fall. But isn't 100 us a little slow for rise/fall
times. Is there any way I can make i t rise/fall faster. At the current
moment I'm leaving the pins unattached to anything and just measuring the
output on an oscilloscope. 

On Jul 20, 8:05=A0am, "TheJokerV" <nick.k...@gmail.com> wrote:
> Hey everyone, I'm working with an MSP430f2012 chip and am tryign to
> generate a delta sigma bitstream using a gpio pin. Unfortunatly whenever =
I
> try to toggle the pin at a rate faster than 10kHz, the pin appears to not
> be able to fully rise or fall. But isn't 100 us a little slow for rise/fa=
ll

Strange. What clock speed are you running at? Which GPIO is it?
Certainly the 2012 can generate *much* faster data rates (orders of
magnitude), are you using the PWM generator or the SPI peripheral? Are
you testing on the T2012 target board or your own design; if your own,
is the chip's Vcc adequately bypassed?

In article <NKudnf_Nhs_jwPnXnZ2dnUVZ_sidnZ2d@giganews.com>, 
nick.kani@gmail.com says...
> Hey everyone, I'm working with an MSP430f2012 chip and am tryign to
> generate a delta sigma bitstream using a gpio pin. Unfortunatly whenever I
> try to toggle the pin at a rate faster than 10kHz, the pin appears to not
> be able to fully rise or fall. But isn't 100 us a little slow for rise/fall
> times. Is there any way I can make i t rise/fall faster. At the current
> moment I'm leaving the pins unattached to anything and just measuring the
> output on an oscilloscope. 
> 
> 
> 
Are you sure that you don't have the pull-up/pull-down resistors enabled 
instead of the outputs?
IIRC, if you do that, then switching the  port output simply changes
from the pull-up to the pull-down resistors.  That would explain the
slow rise and fall times, as the resistors are about 35K Ohms.


That part has a bunch of other logic on Port 1 with the comparator 
inputs, so it looks like there are some extra possibilities for
setting up the port improperly.


I ran into similar problems on an MSP43F248 when I was programming the
pullup and port output to do a bit-banged   open-collector emulation
for an I2C port.


Mark Borgerson