Hey everyone, I'm working with an MSP430f2012 chip and am tryign t generate a delta sigma bitstream using a gpio pin. Unfortunatly whenever try to toggle the pin at a rate faster than 10kHz, the pin appears to no be able to fully rise or fall. But isn't 100 us a little slow for rise/fal times. Is there any way I can make i t rise/fall faster. At the curren moment I'm leaving the pins unattached to anything and just measuring th output on an oscilloscope.
Toggling GPIO Pins very quickly
Jul 20, 2009
2 Replies
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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?
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
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