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Sci.Electronics.Basics -> PIC processor interrupt for delayed output
There are 11 messages in this thread.
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Author: Bill BowdenDate: 22:15 21-04-08
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What is the best approach to generate a delayed output from a trigger
input to a PIC microcontroller? The idea is to have a constant known
time from trigger input to output, so I don't want to poll the logic
level on some pin due to the jitter that would occur. Thought about
using the comparator module to generate an interrupt, but it seems
complicated setting and clearing all the various bits and reference
levels.
Is there an easier way?
-Bill
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Author: Bob MonsenDate: 22:40 21-04-08
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"Bill Bowden" <wrongaddress@att.net> wrote in message
news:77a2a704-f080-4e01-897d-cee2c1f2eb28@h1g2000prh.googlegroups.com...
> What is the best approach to generate a delayed output from a trigger
> input to a PIC microcontroller? The idea is to have a constant known
> time from trigger input to output, so I don't want to poll the logic
> level on some pin due to the jitter that would occur. Thought about
> using the comparator module to generate an interrupt, but it seems
> complicated setting and clearing all the various bits and reference
> levels.
>
> Is there an easier way?
>
> -Bill
You can use the interrupt on change facility. However, you can't poll or
write to the GPIO when you are doing this, because if you happen to be
accessing it, the interrupt flag will not be set. Arrgh. Very annoying bug
in the chip.
See GPIO INTERRUPT in section 12.4.3 in the PIC12F683 manual for more
information.
Regards,
Bob Monsen
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Author: Jon SlaughterDate: 00:20 22-04-08
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"Bill Bowden" <wrongaddress@att.net> wrote in message
news:77a2a704-f080-4e01-897d-cee2c1f2eb28@h1g2000prh.googlegroups.com...
> What is the best approach to generate a delayed output from a trigger
> input to a PIC microcontroller? The idea is to have a constant known
> time from trigger input to output, so I don't want to poll the logic
> level on some pin due to the jitter that would occur. Thought about
> using the comparator module to generate an interrupt, but it seems
> complicated setting and clearing all the various bits and reference
> levels.
Use a timer?
Use a delay circuit that triggers another inteterrupt. Essentially use a cap
and res with the appropriate delay. A pic pin supplies the voltage charging
up the capacitor. Once the cap has reached the appropriate level it triggers
an interrupt pin(needs to be schmitt triggered and the pin that charges the
cap needs to be reset). Probably not the best way but would work well for
very long delays(> s)
Just don't see why you don't use a timer interrupt as it is probably the
most natural method.
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Author: petrus bitbyterDate: 08:21 22-04-08
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"Bill Bowden" <wrongaddress@att.net> schreef in bericht
news:77a2a704-f080-4e01-897d-cee2c1f2eb28@h1g2000prh.googlegroups.com...
> What is the best approach to generate a delayed output from a trigger
> input to a PIC microcontroller? The idea is to have a constant known
> time from trigger input to output, so I don't want to poll the logic
> level on some pin due to the jitter that would occur. Thought about
> using the comparator module to generate an interrupt, but it seems
> complicated setting and clearing all the various bits and reference
> levels.
>
> Is there an easier way?
>
> -Bill
Assuming the trigger not to be synchronous with the PICs clock, you will
always have some jitter. That will be always the case when using
asynchronous systems.
As for the PIC, you did not mention what PIC you have in mind. The usual way
is using the trigger signal to start an interrupt routine. This routine in
turn starts a timer/counter that interrupts when delaytime is over. I see no
use for comparators in this scheme.
petrus bitbyter
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Author: Bill BowdenDate: 14:23 22-04-08
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On Apr 21, 7:40=A0pm, "Bob Monsen" <rcmon...@gmail.com> wrote:
> "Bill Bowden" <wrongaddr...@att.net> wrote in message
>
> news:77a2a704-f080-4e01-897d-cee2c1f2eb28@h1g2000prh.googlegroups.com...
>
> > What is the best approach to generate a delayed output from a trigger
> > input to a PIC microcontroller? The idea is to have a constant known
> > time from trigger input to output, so I don't want to poll the logic
> > level on some pin due to the jitter that would occur. Thought about
> > using the comparator module to generate an interrupt, but it seems
> > complicated setting and clearing all the various bits and reference
> > levels.
>
> > Is there an easier way?
>
> > -Bill
>
> You can use the interrupt on change facility. However, you can't poll or
> write to the GPIO when you are doing this, because if you happen to be
> accessing it, the interrupt flag will not be set. Arrgh. Very annoying bug=
> in the chip.
>
> See GPIO INTERRUPT in section 12.4.3 in the PIC12F683 manual for more
> information.
>
> Regards,
> =A0Bob Monsen
Yes, I notice in the data sheet for the PIC16F628, an on-change
interrupt can be generated from any of 4 pins of PORTB <4,5,6,7> . Any
change will set the RBIF interrupt flag. But it's not clear how to set
it up so it jumps to the service routine when a change takes place. I
imagine the GIE bit needs to be set and maybe some others. There is a
note that the change may be missed if the input is too short, so I
guess it requires a minimum width input.
I might play around with that idea, to see if it works, but it's hard
to simulate in MPLAB, and single step the program. How do I simulate
an interrupt so the program will single step into the service routine?
-Bill
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Author: Bob MonsenDate: 19:16 22-04-08
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> "Bill Bowden" <wrongaddress@att.net> wrote in message
> news:5a45e00f-f5aa-4732-be32-57e23d1e207b@a22g2000hsc.googlegroups.com...
> On Apr 21, 7:40 pm, "Bob Monsen" <rcmon...@gmail.com> wrote:
> > "Bill Bowden" <wrongaddr...@att.net> wrote in message
> >
> > news:77a2a704-f080-4e01-897d-cee2c1f2eb28@h1g2000prh.googlegroups.com...
> >
> > > What is the best approach to generate a delayed output from a trigger
> > > input to a PIC microcontroller? The idea is to have a constant known
> > > time from trigger input to output, so I don't want to poll the logic
> > > level on some pin due to the jitter that would occur. Thought about
> > > using the comparator module to generate an interrupt, but it seems
> > > complicated setting and clearing all the various bits and reference
> > > levels.
> >
> > > Is there an easier way?
> >
> > > -Bill
> >
> > You can use the interrupt on change facility. However, you can't poll or
> > write to the GPIO when you are doing this, because if you happen to be
> > accessing it, the interrupt flag will not be set. Arrgh. Very annoying
> > bug
> > in the chip.
> >
> > See GPIO INTERRUPT in section 12.4.3 in the PIC12F683 manual for more
> > information.
> >
> > Regards,
> > Bob Monsen
>
>
> Yes, I notice in the data sheet for the PIC16F628, an on-change
> interrupt can be generated from any of 4 pins of PORTB <4,5,6,7> . Any
> change will set the RBIF interrupt flag. But it's not clear how to set
> it up so it jumps to the service routine when a change takes place. I
> imagine the GIE bit needs to be set and maybe some others. There is a
> note that the change may be missed if the input is too short, so I
> guess it requires a minimum width input.
>
> I might play around with that idea, to see if it works, but it's hard
> to simulate in MPLAB, and single step the program. How do I simulate
> an interrupt so the program will single step into the service routine?
>
> -Bill
You can set up the stimulus package to wiggle the port value after a timed
delay. However, the stimulus package is pretty hard to figure out. I find it
easier to simply write the program and try it out.
Regarding the interrupt, all you need to do is to set the GIE and GPIE bit,
and watch for GPIF bit being set in the interrupt routine. You can tell the
chip which pins you want to watch using the IOC register.
If you actually are using a PIC12F683, you can use the GP2/INT interrupt,
described in section 12.4.1 of the datasheet. That might be more reliable. I
don't know.
Regards,
Bob Monsen
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Author: google@woodall.me.ukDate: 05:19 23-04-08
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On Apr 22, 3:15 am, Bill Bowden <wrongaddr...@att.net> wrote:
> What is the best approach to generate a delayed output from a trigger
> input to a PIC microcontroller? The idea is to have a constant known
> time from trigger input to output, so I don't want to poll the logic
> level on some pin due to the jitter that would occur. Thought about
> using the comparator module to generate an interrupt, but it seems
> complicated setting and clearing all the various bits and reference
> levels.
>
> Is there an easier way?
>
You don't say what else you want the PIC to be doing while it's
monitoring the pin.
If you can run it in a tight loop I think you can test 8 input pins
(on one port) for a change in four cycles (16 clocks). If you unravel
the loop you can get that down to an average approaching 3 cycles at
the expense of code size.
You also don't say if you're then going to wait in another loop or
whether you'll set up a timer to trigger an interrupt when the output
needs to change state. Finally you don't say how long the delay needs
to be. Unless you can afford your interrupt routine to trash the W and
status register or you can guarantee that the interrupt will never
trigger when anything other than a known bank is selected then there
is quite a lot of overhead you'll need in the interrupt routine that
will limit your minimum delay.
Tim.
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Author: google@woodall.me.ukDate: 05:33 23-04-08
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On Apr 23, 10:19 am, "goo...@woodall.me.uk" <goo...@woodall.me.uk>
wrote:
> If you can run it in a tight loop I think you can test 8 input pins
> (on one port) for a change in four cycles (16 clocks). If you unravel
> the loop you can get that down to an average approaching 3 cycles at
> the expense of code size.
>
Infact, for a single pin I think you can get this down to 3 cycles or
2 cycles with the loop unraveled.
Tim.
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Author: Bill BowdenDate: 21:11 23-04-08
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On Apr 23, 2:19=A0am, "goo...@woodall.me.uk" <goo...@woodall.me.uk>
wrote:
> On Apr 22, 3:15 am, Bill Bowden <wrongaddr...@att.net> wrote:> What is
the=
best approach to generate a delayed output from a trigger
> > input to a PIC microcontroller? The idea is to have a constant known
> > time from trigger input to output, so I don't want to poll the logic
> > level on some pin due to the jitter that would occur. Thought about
> > using the comparator module to generate an interrupt, but it seems
> > complicated setting and clearing all the various bits and reference
> > levels.
>
> > Is there an easier way?
>
> You don't say what else you want the PIC to be doing while it's
> monitoring the pin.
>
It doesn't do anything, just waits for an interrupt in an infinite
loop.
> If you can run it in a tight loop I think you can test 8 input pins
> (on one port) for a change in four cycles (16 clocks). If you unravel
> the loop you can get that down to an average approaching 3 cycles at
> the expense of code size.
>
> You also don't say if you're then going to wait in another loop or
> whether you'll set up a timer to trigger an interrupt when the output
> needs to change state. Finally you don't say how long the delay needs
> to be. Unless you can afford your interrupt routine to trash the W and
> status register or you can guarantee that the interrupt will never
> trigger when anything other than a known bank is selected then there
> is quite a lot of overhead you'll need in the interrupt routine that
> will limit your minimum delay.
>
> Tim.
I got it working, and the interrupt routine calls an output routine
that sets and resets a couple pins according to a calculated delay.
This is what I want, but I'm still not sure what the jitter will be
without putting it on a scope and all that hassel. Using the on-change
interrupt requires the system to continually read the state of PORTB
and generate an interrupt when a change occurs. I don't know how many
clocks that takes and if the change is too fast, (say 100nS pulse), it
may not be seen at all. I'm going to try and overclock it at 25MHz to
reduce the jitter percentage.
Any idea how many clocks are involved monitoring the state of PORTB in
a very tight loop of one line where the program continually goes to
the same line and waits for an interrupt?
-Bill
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Author: google@woodall.me.ukDate: 03:11 24-04-08
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On Apr 24, 2:11 am, Bill Bowden <wrongaddr...@att.net> wrote:
> On Apr 23, 2:19 am, "goo...@woodall.me.uk" <goo...@woodall.me.uk>
> wrote:
>
> > On Apr 22, 3:15 am, Bill Bowden <wrongaddr...@att.net> wrote:> What
is the best approach to generate a delayed output from a trigger
> > > input to a PIC microcontroller? The idea is to have a constant known
> > > time from trigger input to output, so I don't want to poll the logic
> > > level on some pin due to the jitter that would occur. Thought about
> > > using the comparator module to generate an interrupt, but it seems
> > > complicated setting and clearing all the various bits and reference
> > > levels.
>
> > > Is there an easier way?
>
> > You don't say what else you want the PIC to be doing while it's
> > monitoring the pin.
>
> It doesn't do anything, just waits for an interrupt in an infinite
> loop.
>
> > If you can run it in a tight loop I think you can test 8 input pins
> > (on one port) for a change in four cycles (16 clocks). If you unravel
> > the loop you can get that down to an average approaching 3 cycles at
> > the expense of code size.
>
> > You also don't say if you're then going to wait in another loop or
> > whether you'll set up a timer to trigger an interrupt when the output
> > needs to change state. Finally you don't say how long the delay needs
> > to be. Unless you can afford your interrupt routine to trash the W and
> > status register or you can guarantee that the interrupt will never
> > trigger when anything other than a known bank is selected then there
> > is quite a lot of overhead you'll need in the interrupt routine that
> > will limit your minimum delay.
>
> > Tim.
>
> I got it working, and the interrupt routine calls an output routine
> that sets and resets a couple pins according to a calculated delay.
> This is what I want, but I'm still not sure what the jitter will be
> without putting it on a scope and all that hassel. Using the on-change
> interrupt requires the system to continually read the state of PORTB
> and generate an interrupt when a change occurs. I don't know how many
> clocks that takes and if the change is too fast, (say 100nS pulse), it
> may not be seen at all. I'm going to try and overclock it at 25MHz to
> reduce the jitter percentage.
>
> Any idea how many clocks are involved monitoring the state of PORTB in
> a very tight loop of one line where the program continually goes to
> the same line and waits for an interrupt?
It's all in the datasheet - at least for the 16F627 which is the one
I've been playing with.
IIRC the pin is checked on every clock - i.e. provided your pulse is
at least 1 clock it should be picked up. The interrupt is triggered on
the next cycle (cycle is four clocks) - it's not immediately obvious
from the datasheet if the interrupt will trigger on the same clock as
the pin is sampled so your jitter will be between 0 <= t <= 4 clocks
(where one or other of those <= should be <)
Using a tight polling loop
loop:
btfss PORTB,pin
goto loop
That's three cycles so your pulse needs to be at least 12 clocks wide
to guarantee to pick it up and 0 <= t < 12
Unravelling the loop
loop:
btfsc PORTB,pin
goto gotit
btfsc PORTB,pin
goto gotit
...
btfss PORTB,pin
goto loop
gotit:
Then it's usually two cycles but there's one three cycle case so
usually 0 <= t < 8 but worst case 0 <= t < 12 as before.
If you're really worrying about sub microsecond jitter (20MHz PIC
gives you a 200ns jitter) then I'm not sure that a PIC is the right
tool for the job.
20MHz pic gives you 50ns clock time so I'd expect pulses longer than
that to be detected assuming they rise fast enough at the pin.
Tim.
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Author: VaractorDate: 06:19 24-04-08
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On Apr 23, 6:23=A0am, Bill Bowden <wrongaddr...@att.net> wrote:
> On Apr 21, 7:40=A0pm, "Bob Monsen" <rcmon...@gmail.com> wrote:
>
>
>
>
>
> > "Bill Bowden" <wrongaddr...@att.net> wrote in message
>
> >news:77a2a704-f080-4e01-897d-cee2c1f2eb28@h1g2000prh.googlegroups.com...
>
> > > What is the best approach to generate a delayed output from a trigger
> > > input to a PIC microcontroller? The idea is to have a constant known
> > > time from trigger input to output, so I don't want to poll the logic
> > > level on some pin due to the jitter that would occur. Thought about
> > > using the comparator module to generate an interrupt, but it seems
> > > complicated setting and clearing all the various bits and reference
> > > levels.
>
> > > Is there an easier way?
>
> > > -Bill
>
> > You can use the interrupt on change facility. However, you can't poll or=
> > write to the GPIO when you are doing this, because if you happen to be
> > accessing it, the interrupt flag will not be set. Arrgh. Very annoying b=
ug
> > in the chip.
>
> > See GPIO INTERRUPT in section 12.4.3 in the PIC12F683 manual for more
> > information.
>
> > Regards,
> > =A0Bob Monsen
>
> Yes, I notice in the data sheet for the PIC16F628, an on-change
> interrupt can be generated from any of 4 pins of PORTB <4,5,6,7> . Any
> change will set the RBIF interrupt flag. But it's not clear how to set
> it up so it jumps to the service routine when a change takes place. I
> imagine the GIE bit needs to be set and maybe some others. There is a
> note that the change may be missed if the input is too short, so I
> guess it requires a minimum width input.
>
> I might play around with that idea, to see if it works, but it's hard
> to simulate in MPLAB, and single step the program. How do I simulate
> an interrupt so the program will single step into the service routine?
>
RTFM
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