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'[PIC]: Using 2 CCP: Compare failed if Capture even'
2000\10\12@125531 by Wollenberg, Frank

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Hello folks,

I'm using two serial links with a 16C66, one is the internal UART, the other
is implemented using 2 CCPs in a bit-banged fashion. Both are running
interrupt-driven.
My problem is the bit-banged UART.

The receiving part is using one CCP in capture mode for detecting the start
bit. Data bits are then sampled using the SSP.
The transmitter is implemented using the second CCP in compare mode,
set/clear output on match.
Both parts are working as expected as long as i do only transmit or receive.
If i do both the same time (as i must have a full-duplex link), i will get
spurious failure on the transmitter side.

I have examined the problem. If both events - CCP capture interrupt (start
bit detection) and CCP compare interrupt (setup next transmit data) - occur
the same time, the CCP compare module changes the port pin, but the pin goes
into the previous state immediately, so there is a short peak only!!! The
failure is reproducable and documented with an oscilloscope. The falling
edge of the receive line and the edge of the transmit data clock are
simultaniously.

As a quick solution, i have changed the compare module to 'generate sw
interrupt on match' and setup the transmitting port pin in the interrupt
service function. Many jitter is the result. Because of some other complex
interrupt functions, the interrupt latency time can be about 60% of one bit
time. This won't working too. Therefore i have reduced the data rate, but i
can't accept this.

Now my question:
Why will the compare module in the mode 'set/clear output on match' fail, if
the capture module has an event the same time ?
Has anyone had this failure, or similar ?

Before one will reply with some simple solutions, i must say the following:

- I have tested on PICs 16C63, 16C66, 16F876, also with ICE2000 with
PCM16XE1 module. Allways the same failure.
- I have reviewed all data sheets (newest) for the various PICs.
- I have reviewed all errata available (from very old until now).
- I have read various FAQ, news lists, Microchips BBS. No specific
information found.
- The data sheet says, the compare should be configured for special event
trigger. The reason is never discussed. Also i can't do it because of using
timer 1 as a free running timer for other timing issues.
- Microchip says the CCP modules are similar.
- I know, both CCP require timer 1
- Timer 1 is working as a free running timer using the internal clock OSC/4
(timer mode).
- The interaction of multiple CCP modules is discussed well in application
note AN594.
- AN594 appendix E (capt2.asm) uses both CCP in the same way as i have, but
i'm using several other interrupt sources.

Anyway, problems with interacting CCP should be reported. Only some requests
I've found in the net.
Why not open a discussion thread "problem with interacting CCPs" ?

I'm afraid about any replies,
Frank

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2000\10\16@054224 by Wollenberg, Frank

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Hello again,

Several days ago i've sent the (long) message below, but so far nobody
replied. Either no one has discovered this problem or it was my last
sentence of the message. NO NO NO, i'm NOT afraid, i wish to hear from you.
So help me, please.
TIA
Frank

{Original Message removed}

2000\10\16@090745 by Olin Lathrop

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> Several days ago i've sent the (long) message below, but so far nobody
> replied. Either no one has discovered this problem or it was my last
> sentence of the message. NO NO NO, i'm NOT afraid, i wish to hear from
you.
> So help me, please.

I can't say why others didn't reply, but you message was so long that I just
deleted it an went on.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, .....olinKILLspamspam.....cognivis.com, http://www.cognivis.com

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2000\10\16@112407 by M. Adam Davis

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You have been quite thorough in you analysis of the problem.  Chances are those
that read your question didn't answer because they didn't have anything to add.
It would appear that no one else has used the ccp module in the way you are
using it, so asking if anyone else has experienced this will gether few replies.

My own comment is that you should contact your microchip field applications
engineer.  If you don't have one, try contacting Microchip directly.

As a future suggestion, shorter messages seem to gather more responses than
longer detailed ones.  You might have asked for your first question, "I'm using
the CCP modules as an interrupt driven full-deuplex rs-232 transciever.  It
appears as though the two ccp channels are interacting, and I can only do
half-duplex.  Has anyone else had any trouble using one channel as a compare and
the other as a capture simultaneously?"

At that point those with some experience would comment, and ask for more
detailed information.  The key here is to get a few experts hooked on your
thread, and the best way to do that is to ask an easy (short) question.

I'm sorry I can't help with your problem directly.

-Adam

"Wollenberg, Frank" wrote:
>
> Hello again,
>
> Several days ago i've sent the (long) message below, but so far nobody
> replied. Either no one has discovered this problem or it was my last
> sentence of the message. NO NO NO, i'm NOT afraid, i wish to hear from you.
> So help me, please.
> TIA
> Frank
>
> {Original Message removed}

2000\10\16@122140 by Dale Botkin

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On Mon, 16 Oct 2000, Olin Lathrop wrote:

> > Several days ago i've sent the (long) message below, but so far nobody
> > replied. Either no one has discovered this problem or it was my last
> > sentence of the message. NO NO NO, i'm NOT afraid, i wish to hear from
> you.
> > So help me, please.
>
> I can't say why others didn't reply, but you message was so long that I just
> deleted it an went on.

I have a longer attention span, but unfortunately not enough experience
with using the particular features you need help with.

Dale
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2000\10\16@122352 by Olin Lathrop

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> As a future suggestion, shorter messages seem to gather more responses
than
> longer detailed ones.  You might have asked for your first question, "I'm
using
> the CCP modules as an interrupt driven full-deuplex rs-232 transciever.
It
> appears as though the two ccp channels are interacting, and I can only do
> half-duplex.  Has anyone else had any trouble using one channel as a
compare and
> the other as a capture simultaneously?"

Ah, so that's what he wanted.

Note that when two CCP modules are used with one in capture mode and the
other in compare mode, that the compare has to be configured as the special
event trigger, which clears timer 1.  There are also some flakies lurking in
the CCP modules in some chips.  I got caught with a CCP module compare bug
on a 16C77 once, which may be the same circuit as the one in whatever chip
you are using.  I don't remember the details, but you need to check the
errata sheet for the part you are using.

In fact, you should *always* check the errata sheets every time you go to a
new PIC.  I make it a habit to review the errata sheet at the start of every
project, even if I think I'm already familiar with the chip.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, EraseMEolinspam_OUTspamTakeThisOuTcognivis.com, http://www.cognivis.com

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2000\10\17@121332 by Andy Shaw

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----- Original Message -----
From: "Olin Lathrop" <olin_piclistspamspam_OUTcognivis.com>
To: <@spam@PICLISTKILLspamspammitvma.mit.edu>
Sent: Monday, October 16, 2000 5:21 PM
Subject: Re: [PIC]: Using 2 CCP: Compare failed if Capture event the same
time


>
> Note that when two CCP modules are used with one in capture mode and the
> other in compare mode, that the compare has to be configured as the
special
> event trigger, which clears timer 1.

Oh no! Is this really the case? I really wanted to use 2 CCP modules (one
capture one compare) in my next project, but if I have to set them up this
way then it won't work! I wanted to have Timer 1 as a free running timer
(used for lots of things) and have one CCP module measure an input pulse
train and the other generate one. Is this really the case that you *have* to
use the special event trigger stuff in this mode (sigh), anyone know why? Oh
well back to the drawing board (or back of an envelope!). I guess I may be
able to arrange things so that I capture the input then generate the pulse
train (i.e. switch the two CCP modules on/off on the fly).

Andy

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2000\10\17@122457 by Andrew Kunz

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Andy,

You can still use them as you want I think.  I suspect you want to read a servo
pulse in, modify it, and send it out.

If that's the case, you are fine.

Instead of using compare, use one for capture, one for PWM.

The capture one you operate by watching for high, then for low.  The capture
input value will give you what Timer1 was at the time of the rising/falling
edge.  You only need to subtract to find the pulse width.

For the output channel, you can simply tell it to generate the pulses as you
want.  They will be all synched to TMR0 = 0.

Also, timing is not especially critical on either of these things - no need to
do it in an interrupt if you aren't really busy.  The values will be retained
until the next change.

Think about using TMR2 as a frame timer...

This is what I did for several of my products, and it works fine.

Andy

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2000\10\17@163539 by Olin Lathrop

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> > Note that when two CCP modules are used with one in capture mode and the
> > other in compare mode, that the compare has to be configured as the
> special
> > event trigger, which clears timer 1.
>
> Oh no! Is this really the case? ...

According to the manual for the 16F87x it is.  See "Table 8-2: Interaction
of two CCP Modules" on page 57.  This may be different on other PICs - I
haven't looked.  I also haven't personally played with this, but there is
little reason to doubt such a direct assertion in the manual.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, spamBeGoneolinspamBeGonespamcognivis.com, http://www.cognivis.com

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2000\10\18@010733 by Andy Shaw

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Hi Andy,
Almost a correct guess. What I'm actually doing is using the capture input
to read from and Analog devices accelerometer (which generates a PWM style
output prop to the G force). But yes the compare part of the CCP is being
used to generate an RC pulse! Actually I think I can simply switch between
the two (I have the time available), I want to keep the two PWM chans to
generate a set of PWM outputs for speed control!

Thanks
Andy


{Original Message removed}

2000\10\18@052307 by Wollenberg, Frank

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> According to the manual for the 16F87x it is.  See "Table 8-2: Interaction
> of two CCP Modules" on page 57.  This may be different on other PICs - I
> haven't looked.  I also haven't personally played with this, but there is
> little reason to doubt such a direct assertion in the manual.

As i have described in my first message and different to that noted by the
manual and AN594, interaction of two CCP modules, one in capture and the
other in compare mode software interrupt only, works. I'm using the capture
for start bit detection, the compare for transmitting bit-per-bit. Tested
with 16C63, 16C66, 16F873 and various emulators.

The problem i've described, is capture together with compare, set/clear
output on match.
> If both events - CCP capture interrupt (start
> bit detection) and CCP compare interrupt (setup next transmit data) -
occur
> the same time, the CCP compare module changes the port pin, but the pin
goes
> into the previous state immediately, so there is a short peak only!!!
The compare fails if a capture event occurs the same time. Raising the
frequency from 4 to 20 MHz, the number of failures drops significant. I've
tried again capt2.asm from AN594 with some changes, and it works.
So i've played with my serial module and i've found the bug, i think so far.
In the capture routine, i do read timer1 to eleminate the latency time. For
simplicity, Timer1 is stopped, read and restart. If i don't stop timer1, the
module works. I will test this furthermore.

Hint: Don't stop timer1 if you use capture and compare with set/clear output
on match !!!

Frank
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2000\10\18@075129 by Andrew Kunz

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>Almost a correct guess. What I'm actually doing is using the capture input
>to read from and Analog devices accelerometer (which generates a PWM style
>output prop to the G force). But yes the compare part of the CCP is being
>used to generate an RC pulse! Actually I think I can simply switch between
>the two (I have the time available), I want to keep the two PWM chans to
>generate a set of PWM outputs for speed control!

First, make sure you can get the part of Analog if you are making more than one.
They are really hard to get right now (I have several on order since May and
they're telling me April 2001) and will cost a lot more than they quoted
earlier.

I have used this exact setup.  Works great!

You can keep the one input always set to the ADXL device and integrate the
results constantly (hint hint).

The PWM output you can switch back and forth between two servos using a logic
chip (demux).  Then you can update them as frequently as you want.  I had a
design using a GAL to use the two channels as inputs, then flip one pin and some
software to turn them into outputs, and they would go out on another two pins
from the GAL.  Super-accurate mixing, only used 3 pins to get 2 inputs and 2
outputs with .5uS resolution.  The logic was all very fast and short code,
leaving lots of codespace to do things like variable mix ratios, expo, etc.

Andy

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2000\10\19@091806 by Andy Shaw

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Got to ask Andy. What was the application? Can you say? Sounds interesting!
I'm thinking of using the accelerometer for Tilt input but so far it seems
sort of marginal in terms of resolution (I'm using the slightly older 2G
sensor not the latest updated E version - I picked up a few a while ago and
have just got around to using them).

BTW have you ever used any of this stuff in any of those fast targets err
surface craft you like to play around with. Is it possible to add any sort
of stability enhancement (or would that spoil all of the fun...).

Andy

{Original Message removed}

2000\10\19@094058 by Martin Hill

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I have used them to measure vehicle performance, have a look at
the performance meter at http://www.ac22.com  What sort of resolution
are you looking for?  If you set the filter capacitors to give a slow
enough response you should be able to resolve to 5mg.

Martin
{Quote hidden}

> {Original Message removed}

2000\10\19@094638 by Alan B. Pearce

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>I have used them to measure vehicle performance, have a look at
>the performance meter at http://www.ac22.com  What sort of resolution

You should be hawking these around the TV stations and insisting they use them on the motoring programs when they test cars! ;))

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2000\10\19@095716 by Martin Hill

picon face
Give me a chance, we have only been selling them for three
months, there are various reviews lined up in car magazines
though.  New version will be out in a couple of weeks with data
storage and RS-232 interface.

PIC Content

The system works using the two CCP channels to measure the
pwm signals from the accelerometer, it uses a 16F876 operating at
16MHz, data is stored on an 8k i2c eeprom, power supply is done
using a step up regulator from 2 x 1.5v AA batteries (MAX619)

If using the ADXL202 be very careful with noise on the supply lines.
Take special care to ensure the supply is as clean as possible.
{Quote hidden}

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2000\10\19@113022 by Andy Shaw

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Hi Martin,
Nice looking application. As to the resolution good question. Maybe Andy K
has some thoughts on this. I've never really determined how far you need to
go. My current system (using an electrolytic tilt sensor) probably gives
about 0.1 degree or so (maybe even better). Not sure exactly how good it
needs to be though.

I also noticed the problems with the power supplies for the device. Just
having a R/C Servo on the same Bench power supply seems to create all sorts
of problems!

Andy

{Original Message removed}

2000\10\19@152901 by Chris Carr

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>I have used them to measure vehicle performance, have a look at
>the performance meter at http://www.ac22.com  What sort of resolution

You should be hawking these around the TV stations and insisting they use
them on the motoring programs when they test cars! ;))


It looks impressive but it will never replace Jeremy Clarkson.. Which
reminds me Motormouth's Chat Show starts again tonight on Beeb 2 at 10pm.

Have we moved in [OT:] Territory ?

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2000\10\19@154723 by Sean H. Breheny

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Hi Martin,

On your page, you say that the AC22 can measure power at the wheels. How
can it do that by just measuring acceleration? I could see how it could get
initial power, but once you are going at any non-negligible speed, won't
some of the wheel torque will go into counteracting drag and fail to
contribute to the acceleration?

Sean

At 02:39 PM 10/19/00 +0100, you wrote:
>I have used them to measure vehicle performance, have a look at
>the performance meter at http://www.ac22.com  What sort of resolution
>are you looking for?  If you set the filter capacitors to give a slow
>enough response you should be able to resolve to 5mg.
>
>Martin

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2000\10\20@043510 by Martin Hill

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Indeed it does, which is why two vehicle parameters are CdA x
Frontal area and Rolling Resistance.  If you know the mass, speed
and these two, you can calculate the power to overcome rolling
resistance and aerodynamic drag.  This is something I have never
seen on any other accelerometer based performance meter.

Martin

{Quote hidden}

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2000\10\20@082039 by Andrew Kunz

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>Got to ask Andy. What was the application? Can you say? Sounds interesting!

Application with integrating accelerometer - can't say right now, but it applies
to model airplanes and is totally passive.

>BTW have you ever used any of this stuff in any of those fast targets err
>surface craft you like to play around with. Is it possible to add any sort
>of stability enhancement (or would that spoil all of the fun...).

I ran my Patriot (http://www.rc-hydros.com/patriot.html) at the Nationals.  It was
built for one, to use in pitch control.  I chickened out of using it at the last
minute, and just locked the servo into my third channel (I was mixing third
channel (pitch) plus ADXL to stabilize the boat).  As it turned out, I was
glitched just after the start and the impact snapped off the canard.  I ran the
rest of the heat at full-bore, trying to catch the leaders, and ended in 4th
place.  I have video of it on my CD "catalog", but not on the net (too much
space used already).

I chickened out because I hadn't had test time.  Testing means hooking up the
boat on a pivoting mechanism, hooking that on a pickup truck, and going for a
drive at 40MPH to see how it responds.  I don't think it will be especially
useful on this boat, as I designed the aerodynamics to avoid the buildup in the
first place.  The only time it blew off was in testing, with the CG about 6"
back from where it belongs.  The only other time it launched was when I hit a
buoy, and that made a nice little airplane flight!


> from the GAL.  Super-accurate mixing, only used 3 pins to get 2 inputs and
2
> outputs with .5uS resolution.  The logic was all very fast and short code,
> leaving lots of codespace to do things like variable mix ratios, expo,
etc.

This design was a elevon/v-tail mixer.

Andy

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2000\10\20@091643 by Andrew Kunz

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>Nice looking application. As to the resolution good question. Maybe Andy K
>has some thoughts on this. I've never really determined how far you need to
>go. My current system (using an electrolytic tilt sensor) probably gives
>about 0.1 degree or so (maybe even better). Not sure exactly how good it
>needs to be though.

I'd have to look at the code again, but my memory says 1/2 degree was what we
de-tuned it to.

>I also noticed the problems with the power supplies for the device. Just
>having a R/C Servo on the same Bench power supply seems to create all sorts
>of problems!

LC isolate the PIC power from the servos.

Andy

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2000\10\20@093824 by Andy Shaw

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----- Original Message -----
From: "Andrew Kunz" <RemoveMEakunzspam_OUTspamKILLspamtdipower.com>
To: <RemoveMEPICLISTTakeThisOuTspamspammitvma.mit.edu>
Sent: Friday, October 20, 2000 1:20 PM
Subject: Re: [PIC]: Using 2 CCP: Compare failed if Capture event the same
time


>
> I ran my Patriot (http://www.rc-hydros.com/patriot.html) at the Nationals.  It
was
> built for one, to use in pitch control.

Nice looking boat Andy. Pity about not using the auto pitch control, it
would have made a great story! By the way is sort of thing allowed in
racing, do think it will continue to be after you win!

Andy

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2000\10\20@094035 by Andy Shaw

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----- Original Message -----
From: "Andrew Kunz" <EraseMEakunzspamspamspamBeGonetdipower.com>
To: <RemoveMEPICLISTKILLspamspammitvma.mit.edu>
Sent: Friday, October 20, 2000 2:14 PM
Subject: Re: [PIC]: Using 2 CCP: Compare failed if Capture event the same
time
>
> LC isolate the PIC power from the servos.
>

Any advice on a good setup for this (components/values etc.)?

Andy

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2000\10\20@100826 by Andrew Kunz

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I have been using 390uH and 220uF - that's heavy overkill, though.  Because
that's what I have handy.

Andy









Andy Shaw <andysSTOPspamspamspam_OUTSCO.COM> on 10/20/2000 09:33:32 AM

Please respond to pic microcontroller discussion list <spamBeGonePICLISTSTOPspamspamEraseMEMITVMA.MIT.EDU>








To:      KILLspamPICLISTspamBeGonespamMITVMA.MIT.EDU

cc:      (bcc: Andrew Kunz/TDI_NOTES)



Subject: Re: [PIC]: Using 2 CCP: Compare failed if Capture
         event the same              time








{Original Message removed}

2000\10\20@103124 by Andrew Kunz

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It _would_ have made a great story, but without test time it would probably have
been a tragedy or comedy, not the Hero Wins type of drama.  It was the biggest
boat on the course (one of 4 big boats, the others were all 2" shorter) and one
of the lightest.

Andy









Andy Shaw <EraseMEandysspamEraseMESCO.COM> on 10/20/2000 09:31:24 AM

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cc:      (bcc: Andrew Kunz/TDI_NOTES)



Subject: Re: [PIC]: Using 2 CCP: Compare failed if Capture
         event the same              time








{Original Message removed}

2000\10\20@154330 by M Ore

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Hi,
 Andy you mentioned you were doing this type of thing with Electrolytic
tilt meters. Do you know if these are better than the analog accelerometers
in measureing pitch and roll?  And who makes the Elec.tilt ones you use? My
application is along the VR lines.

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2000\10\23@093556 by Andy Shaw

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As always each has advantages/disadvantages. I've been playing around with
both this weekend. The accelerometer seems to work fine if you can give it a
good supply and you can read lots of samples and process them to reduce some
of the jitter and noise. The Electrolytics take a bit more working with
(more pins and you need to take care over the way you drive them). But you
probably have more control over the characteristics (you can get different
types of fluid, different sizes etc.). I think that if you want to measure
really small angles of tilt then the electrolytic ones are the way to go,
but for ease of interface the accelerometers are better. Just my thoughts
anyone else want to join it?

Andy

BTW: I got my sensors from Skip Asay of http://www.rcboats.com which he let me have
as a favour, but http://www.aositilt.com seem to have something that looks very
much like the sensors I use.

{Original Message removed}

2000\10\30@130631 by Wollenberg, Frank
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Hi all,
as a result of my tests with capture and compare working together, i get the
following answers:

1)      capture module is working with all configurations of the compare
module
2)      compare module is working with generate interrupt on match only
3)      compare module is working with set/clear output on match only if
timer1 is not stopped temporarely

Case 3 was my big mistake. I've stopped timer1 in the capture service
routine for reading him.
I have contacted my local FAE for further information (from Microchip?).

Thanks to the great piclist community.

Frank
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2000\10\30@235210 by James Kelley

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I have only received a couple of email on the piclist. Is the list still
active?
----- Original Message -----
From: "Wollenberg, Frank" <TakeThisOuTF.WollenbergKILLspamspamspamGSP-BERLIN.DE>
To: <.....PICLISTspamRemoveMEMITVMA.MIT.EDU>
Sent: Monday, October 30, 2000 12:08 PM
Subject: Re: [PIC]: Using 2 CCP: Compare failed if Capture event the same
time


> Hi all,
> as a result of my tests with capture and compare working together, i get
the
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2000\10\31@084708 by Andy Shaw

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Hi Frank,
I've been trying to work this one out. I've been using a compare on one
module (generating both rising and falling edges), while using the other
module in capture mode. So far no problems. The documentation on this is
really confusing. Seems to me the only time that using compare and capture
at the same time is if you use the mode that resets the timer.... Anyone
else got any info on this. Have I just been lucky so far?

Andy

{Original Message removed}

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