PIC PortA and PortB not working the same.

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Nigel Goodwin

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I'm using a PIC18F27K42, and part of the project requires an audio indication (beep), originally I had a piezo sounder across RA2 and RA3, bridged to make it louder. This worked perfectly well, but I was running low on I/O so thought - I'll move the piezo to RB6/RB7 instead (the ICSP pins) - and added header pins so I could connect or disconnect the piezo in case it wouldn't program with it there (and it wouldn't).

But, when I connect the piezo in circuit and the beep is called it makes a click and everything just locks up.

I've cured it by adding a 220 ohm resistor in series with the piezo, which also allows the ICSP to work - but I can't see any difference between PortA and PortB pins, so has anyone any ideas?. Doesn't really matter, because I've cured the issue - but I'm just puzzled about it?.

If anyone is interested?, I generate the 'beep' with a timer interrupt, set by this line:

Set_Beep(3, 100);

The 3 is one of a number of preset frequencies, done that way so I can alter the frequencies of a particular 'beep' all in one go (just alter the timer value that 3 refers to), and the 100 is the time of the beep in mS - you just call the routine and it runs transparently in the background.
 
Are you doing this with the ICSP connected?
Most programmers have a 4.7K pulldown on the ICSP clk and data lines.

Are you changing the PORTx reg or the LATx reg settings?
Show the couple of lines that twiddle the RB6/RB7 pins so we can see how you're doing it.
 

No, I unplug the programmer once it's programmed.

I use LATx, as below:

C: 
// section from setup
#define TONE            LATBbits.LATB6      // output pin for beep
#define TONE2           LATBbits.LATB7      // output pin for bridged beep

// section from ISR
else if (PIR4bits.TMR1IF)
    {
        if (beep)
        {
            TONE = !TONE;
            TONE2 = !TONE;      // for louder bridged output
        }   
            else   
        {       
            TONE = 0;
            TONE2 = 0;
        }
        TMR1_WriteTimer(timer1ReloadVal);
        PIR4bits.TMR1IF = 0; /* Clear Flag */
    }
 
Ian Rogers said:
Just check your IDE as it defaults to debug... There is a release/ debug combo box..
I hardly use release version..
Click to expand...
I don't know where that might be?, and can't find it on MPLABX 6.0 - but all the hex files etc. are labelled as production, and the debug folder is empty.
 
OH I see.... I haven't used MPLABX for some time... They have a menu for debug and a menu for production.... The little hammer icon has a dropdown menu...
 
Code: 
#define TONE            LATBbits.LATB6      // output pin for beep
#define TONE2           LATBbits.LATB7      // output pin for bridged beep

 TONE = !TONE;
 TONE2 = !TONE;      // for louder bridged output
There's going to be a short amount of time where the IO pins are fighting each other, depending on what the compiler generates for that, and with XC8 it's quite a few instructions.

If you want them to toggle at the same time try something like:
Code: 
LATB ^= 0xc0;

Electrically, all of those IO pins are spec'd the same so I can't see a difference from that end of things. I guess it just didn't like the direct load from the piezo for whatever reason.
 
Ian Rogers said:
OH I see.... I haven't used MPLABX for some time... They have a menu for debug and a menu for production.... The little hammer icon has a dropdown menu...
Click to expand...
Just had a luck, it still does

Debug is the second option down, the third one is Pro Comparison - presumably trying to sell you the expensive Pro compiler?.
 
Remember! I have the pro version so Debug and production compile the same.. But I hardly ever use the programming pins, so I don't worry about that... I also don't use MPLAB, I use VSM inside Labcenter...
That has the button DEBUG / RELEASE...
 
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