Generating precise non periodic digital waveform using MCF52235 MPU

ariaveta — Wed, 02 Apr 2008 03:59:08 GMT

Hello,

I need to generate a digital non periodic waveform on an output pin of the MCF 52235 MPU and CW 6.3.

First, I tried using QSPI, but i discovered that I cannot generate burst longer than 16 pulses without delays between them; then I tried disabling interrupts and using GPIO driven from assembler instructions... but, again, no luck because the GPIO module clock is not correlated with main processor clock, so there is a random skew in the generated waveform (2 or 4 CPU clock skew).

Now, I'm trying using DMA timer.. I plan to store the waveform in RAM as a buffer of delays, then start the timer and allow it to read the counter register from the buffer using DMA. This way, maybe, I'll get the waveform. But there's no code example showing how to use DMA timers. I searched the documentation and the forum and I found nothing.

Could someone please help me, maybe posting some code fragment?

Any suggestion will be appreciated,
Thanks,
Marco

Re: Generating precise non periodic digital waveform using MCF52235 MPU

bkatt — Thu, 03 Apr 2008 00:02:42 GMT

It seems that the General Purpose Timer (GPT) is designed to do this sort of thing, not the DMA timer. I don't have any code for you, but I think you would set it up to toggle on output compare, then go into a loop or interrupt sequence that waits for the timer compare event, then adds the next delay interval to the compare register.

topic Re: Generating precise non periodic digital waveform using MCF52235 MPU in ColdFire/68K Microcontrollers and Processors

Generating precise non periodic digital waveform using MCF52235 MPU

Re: Generating precise non periodic digital waveform using MCF52235 MPU