Lpc2000

Thank You Karl for the valuable Insite.
  Alexander K.Carey

Karl Olsen <kro@...> wrote:
  --- In lpc2000@yahoogroups.com, "alvingoesdown" <alvingoesdown@...> 
wrote:

> The External Match Register Uses the EMO-EM3 as outputs bits 0,1,2,3
> The documentation states These bits reflect the state of the
> outputs, If thats the case then you should not write to these bits 
> correct????
> So the LSB 0-3 should not be written to in the external match
> register correct.??? I'm lost on this one?? 
> Anybody got any idea on how or just what the purpose of these bits
> are other than just an output pin that goes high, low, or toggle????
> I can see reading these bits for status of the output, but writting
> to these bits I don't understand unless it's an enable, but if thats
> the case, then how can you read the output status???

When a pin is configured as MATx.x, you can actually control it by 
writing to its EMx bit.  You can e.g. set it high by writing 1 to the 
EMx bit, and configure the EMCx bits and a match register to clear it 
at a specific timer value.

I have used this when I needed an extra PWM output and had already 
used the PWM timer: In a jitter-free FIQ handler (see msg 12652), 
configure EMR to set MATx.x high now and low on a MRx match.  It 
works nicely, but you are right that the MATx.x outputs are not that 
useful.  In the LPC2101/2/3, a PWM feature is added so you can use 
the MATx.x pins as real hardware PWM outputs.

Karl Olsen






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