Hi,
perfect 50.000000% is not reachable, in no way. You will come nearest to that
number by starting the A/D conversion very early in the only ISR, doing the
jittering stuff after the conversion is startet. You will not get less jitter
by moving the conversion to the main program, as the main program is suspended
while the ISR is running. Remember that it doesn't matter at what time you're
reading the ADC, it only matters at what time you're starting the conversion.
Or, depending on the chip you're using: e.g. the 18f27k42 has an "Auto
Conversion Trigger", which can start a conversion on a selected event, like
timer rolling over or PWM output. No interrupt needs to be fired here to start
a conversion, so that is the way to get really, really close to "perfect 50%".
Greets,Kiste
Am Sonntag, 3. April 2022, 19:07:52 MESZ hat vsurducan
<[email protected]> Folgendes geschrieben:
Hi all,I'm trying to have a fast bidirectional control between the ISR and
main loop without much success. Everything goes ok if in the main loop I use
the IE registers flags to stop or start things in the ISR. It seems to not work
ok if I try to control things in the main loop by reading registers which are
changed in the ISR.
In the ISR I'm toggling one bit on and off each time the tmr1 is rollowing.
This is generating a 50% duty cycle signal which I need to control two power
solid state switches A and B. The max toggling frequency is around 8KHz. There
is a delay of 2us between switching, both switches have less than 1us latency
between ON-OFF and OFF-ON states on the hardware side, the hardware is running
ok.
In the main loop I'm reading a voltage and a current controlled by the A and B
switches by reading first the ISR toggled bit and then initiating an ADC
measurement. Even the Tcy speed is enough (48MHz clock), sometimes the ADC
current and voltage values correspond to a wrong switch A and B position...and
this is annoying. I did not read the ADC in the ISR because I need a perfect
50% duty cycle and a lot of other things are happening in the ISR adding a
jitter....but perhaps this is the only way?
Any good ideas?
BTW, ( this is another story) during USB serial communication ( interrupt or no
interrupt driven) the other fast processes have to be stopped...and the GIE
flag can not be turned off for a short time in the main loop because connection
is lost...
thx,
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