You have a huge noise there, try to see why. Almost 2Vpp of noise is a real mess. It's possible that sometime the PWM dutycycle be longer that PWM period? Only then the CCP output remains high. Maybe a compiler problem ? Wesley-Basil-Vasile On 5/12/08, Gordon Williams wrote: > Hi All, > > I'm having problems tracking down the reason of some glitches occurring on > the CCP1 output and it is driving me a bit crazy. > > I'm putting some smarts into a basic RC transmitter. I've replaced the > current chip producing the pulse train to the RF section with a daughter > board and added a cell phone LCD, some switches and Serial port for input > and output. The serial port and LCD (spi) work fine and they don't have any > glitches. The 5 ADC readings for the joysticks (4) and battery voltage also > work well with only 1 bit of noise on a 10 bit reading (referenced to the > power and gnd lines). > > The PIC that I am using is the 16F886. Its supply is a 78L05 on the main > board and I have a 10uf Tant and three 0.1uF on the power lines on the > daughter board. The daughter board is single sided with a ground plane pour > under the PIC and every else where I could. Because I don't have ADC > problems or serial or spi errors that noise must be reasonably constrained, > I think. > > I'm using CCP1 (pin C2) to produce the PPM that goes to the RF section. It > is the standard PPM protocol (each channel pulse is 1 to 2 ms wide including > the following 0.3 ms pulse, repeated every 20ms). > > Timer1 runs freely. With a CCP1 interrupt (my only interrupt) I update > CCPR1 with the duration until the next transition high or low and the > CCP1CON bits to set the next transition in the correct direction. My main > program clears a flag and that is all. > > Most of the time it works perfectly and looks like: > http://www.cyberus.ca/~g_will/TxGlitch/NoGlitch1.jpg > > or detail > > http://www.cyberus.ca/~g_will/TxGlitch/NoGlitch.jpg > > The receiver pulses for the first 4 channes are shown in the logic section > below. > > Every 20 to 100 frames on average (sometimes they are consectutive frames) I > get a glitch: > > http://www.cyberus.ca/~g_will/TxGlitch/Glitch1.jpg > > or > > http://www.cyberus.ca/~g_will/TxGlitch/Glitch2.jpg > > The green lines indicate where the signal should have been. > > There is a fair bit of noise - about 1.8 volts p-p because the scope ground > was attached to the battery neg lead. I don't think that my probes are very > well shielded either. The noise is from the 72 Mhz RF. > > In each case the low output flips high. My question is WHY? > > Timer 1 keeps on rolling as there is no problem with frame spacing or the > width or placement of the next good pulse. > > CCPR1 is not upset or incorrectly set for the same reasons - because the > next good pulse is in the proper location relative to the last good pulse. > > The serial and LCD have been comment out. I'm reading 2 ADC on port A and > 3ADC on port B. All other pins on ports A,B,C are inputs and some are > floating (could this be a problem?) > > Is there anything else on the chip that may be miss-configured that may be > giving me a problem? > > The chip docs say: > Note: Clearing the CCP1CON register will force > the CCPx compare output latch to the > default low level. This is not the PORT I/O > data latch. > > But I don't think that this applies to me. The only time that I do anything > with the CCP1CON is during the long bit in the frame between the pulse > series and the glitch doesn't always happen there. > > It is not read-mod-write ... I'm not writing anything to the port. > > I read the errata - nothing there indicated a problem. > > Any ideas what I should be looking at/ trying next?? > > - I guess I should look at the 5 v power going to the chip to see that it is > truly quiet and doesn't have a spike. Brown out is disabled. > > - Should set the un-used outputs to either high or low. - Good right? > > Funny that it is only affecting one pin that I can see. > > Looking for suggestions... > > Regards, > > Gordon Williams > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist