Running a pic18F45K20 at full speed

To run at full speed you need to enable the internal HS Oscillator to run at 16Mhz and the x4 PLL

When running at 64Mhz I don't believe you can have the clock output on pin RA6, but your config (FOSC=INTIO7) has the clock going out on RA6

Unfortunately I am not at my dev machine at the moment, so I can't give you the C Compiler macros you need to use for #pragma config... but I know that it is not INTIO7

You need to have bits 3 to 0 of register CONFIG1H set to  0110 to enable the 16Mhz internal oscillator AND enable the x4 PLL

You also need to set bits 5 to 0 in the OSCTUNE register to 011111 t set the internal oscillator to maximum frequency and then bit 6 of OSCTUNE to 1 to enable the PLL

There may well be compiler macros you can use in #pragma config to set all these options for you - but like I say I can't check them for you at the moment.

You should also check out the data sheet (http://ww1.microchip.com/downloads/en/DeviceDoc/41303G.pdf) and look at the registers CONFIG1H and OSCTUNE

I haven't looked at your I2C code yet - but I recently completed a product with PIC18F46K20-E/PPIC18F46K20-E/P and I2C components (oled displays) - but I wrote my own library to do it and bit-banged it out on pins other than the dedicated I2C pins and it worked a treat.

I hope this helps.

Message was edited by: Kenny Millar

Thanks Kenny, I have set the: #pragma config FOSC = HSPLL, however now the pic doesnt run at all, making me think this is for an external crystal only?  My updated code is:

/** C O N F I G U R A T I O N   B I T S ******************************/

#pragma config FOSC = INTIO7, FCMEN = OFF, IESO = OFF                        // CONFIG1H
#pragma config PWRT = ON, BOREN = OFF, BORV = 30                            // CONFIG2L
#pragma config WDTEN = OFF, WDTPS = 1                                       // CONFIG2H
#pragma config MCLRE = OFF, LPT1OSC = OFF, PBADEN = OFF, CCP2MX = PORTC     // CONFIG3H
#pragma config STVREN = ON, LVP = OFF, XINST = OFF                          // CONFIG4L
#pragma config CP0 = OFF, CP1 = OFF, CP2 = OFF, CP3 = OFF                   // CONFIG5L
#pragma config CPB = OFF, CPD = OFF                                         // CONFIG5H
#pragma config WRT0 = OFF, WRT1 = OFF, WRT2 = OFF, WRT3 = OFF               // CONFIG6L
#pragma config WRTB = OFF, WRTC = OFF, WRTD = OFF                           // CONFIG6H
#pragma config EBTR0 = OFF, EBTR1 = OFF, EBTR2 = OFF, EBTR3 = OFF           // CONFIG7L
#pragma config EBTRB = OFF                                                  // CONFIG7H

/** I N C L U D E S **************************************************/
#include "p18f45k20.h"
#include "07 ADC.h"  // header file
#include "delays.h"
#include "i2c.h"

//#include "math.h"
//#include "08 Interrupts.h"  // header file ****throws error

/** Prototypes**/
void main(void);
unsigned char I2C_SendByte(char myVolume);//char myByte)
unsigned char IncrementGrey(unsigned char Value); unsigned char DecrementGrey(unsigned char Value);
/** V A R I A B L E S *************************************************/
#pragma udata   // declare statically allocated uinitialized variables

/** D E C L A R A T I O N S *******************************************/
#pragma code    // declare executable instructions

/*******Global Variables******************/

/**********************************/
void main(void)
{

/******************************************************************/
  //OSCCON*****************
// IDLEN IRCF2 IRCF1 IRCF0 OSTS(1) IOFS SCS1 SCS0

OSCCONbits.IDLEN     = 0;    // Not enable pherimetral during sleep()
//Internal Frequency selection bits
OSCCONbits.IRCF2     = 1;    // 16 Mhz selected, 110=8Mhz
OSCCONbits.IRCF1     = 1;
OSCCONbits.IRCF0     = 1;
WDTCONbits.SWDTEN    = 0; // Disable Watchdog
// OSCTUNE***************
OSCTUNEbits.TUN0  = 1;
OSCTUNEbits.TUN1  = 1;
OSCTUNEbits.TUN2  = 1;
OSCTUNEbits.TUN3  = 1;
OSCTUNEbits.TUN4  = 1;
OSCTUNEbits.TUN5  = 0;
OSCTUNEbits.PLLEN = 1; // Enable PLL //PLL enabled for INTOSC (4 MHz and 8 MHz only)
OSCTUNEbits.INTSRC= 1;// PLL for 31khz option when selected
  //(SCS)System clock select bits:
OSCCONbits.SCS0      = 0; //  // Internal oscillator selected
OSCCONbits.SCS1      = 0;    //
//scs: 00 = Primary clock (determined by CONFIG1H[FOSC<3:0>]).
//Clock Status bits:
while(OSCCONbits.OSTS == 0){}       //Oscillator Start-up Time-out Status bit
while(OSCCONbits.IOFS == 0){}       //INTOSC Frequency Stable bit       
/******************************************************************/
    // Init I/O
    TRISD = 0x00;              // PORTD bits 7:0 are all outputs (0)
    TRISB = 0xFF;             // PORTB (Encoder) are all inputs (1)
TRISC = 0xFF;
INTCON2bits.RBPU = 0;  // enable PORTB internal pullups
INTCONbits.GIEL  = 0;
INTCON2bits.INTEDG1 = 0;
INTCON3bits.INT1IP = 0;
INTCON3bits.INT1IE = 1;
INTCON3bits.INT1IF = 0;
RCONbits.IPEN = 1;

WPUBbits.WPUB0 = 1;   // enable pull up on RB0
/*********************************************************************/
PA=NAPA=PORTD=0;
volume=0xFF;PORTD=0x44;

//generate squarewave.....
  while (1){PORTD=0xFF;Nop();Nop();PORTD=0x00;}
}

The code above generates a 16Mhz signal on RA6 (as expected: 64Mhz/4=16Mhz), but the squarewave output is just 2,7Mhz??

Hi John,

In order to narrow down your problem, I suggest you first write a very simple program that blink an LED every second based on a timer.

This will help making your hardware stable.

Can you post your board schematic or give a link if it is an existing commercial board ?

What is your Vdd ?

Did you put some capacitors around your oscillator ? which value ?

How about your Reset circuit ?

How do you program your PIC ?

regards

Hi, I am using the 44-pin pickit development board with the said processor which has decoupling capacitors on there I believe, I am using the ICD3 with it however.

The program works, except for getting a 64Mhz clock, I have extracted the configuration lines to make it easier for you:

/** C O N F I G U R A T I O N   B I T S ******************************/

#pragma config FOSC = INTIO67, FCMEN = OFF, IESO = OFF                        // CONFIG1H

void main(void)
{

WDTCONbits.SWDTEN    = 1; // Disable Watchdog
// OSCTUNE***************
OSCTUNEbits.TUN1  = 1;
OSCTUNEbits.TUN2  = 1;
OSCTUNEbits.TUN3  = 1;
OSCTUNEbits.TUN4  = 1;
OSCTUNEbits.TUN5  = 1;
OSCTUNEbits.PLLEN = 1; // Enable PLL //PLL enabled for INTOSC (4 MHz and 8 MHz only)
OSCTUNEbits.INTSRC= 1;
//OSCCON*****************
// IDLEN IRCF2 IRCF1 IRCF0 OSTS(1) IOFS SCS1 SCS0

OSCCONbits.IDLEN     = 0;    // Not enable pherimetral during sleep()
//Internal Frequency selection bits
OSCCONbits.IRCF2     = 1;    // 16 Mhz selected, 110=8Mhz
OSCCONbits.IRCF1     = 1;
OSCCONbits.IRCF0     = 1;
//CONFIG1H = 6;
  //(SCS)System clock select bits:
OSCCONbits.SCS0      = 1; //  // Internal oscillator selected
OSCCONbits.SCS1      = 0;    //
//scs: 00 = Primary clock (determined by CONFIG1H[FOSC<3:0>]).
//Clock Status bits:
while(OSCCONbits.OSTS == 0){}       //Oscillator Start-up Time-out Status bit
while(OSCCONbits.IOFS == 0){}       //INTOSC Frequency Stable bit       
/******************************************************************/
    // Init I/O
    TRISD = 0x00;              // PORTD bits 7:0 are all outputs (0)
    TRISB = 0xFF;             // PORTB (Encoder) are all inputs (1)
TRISC = 0xFF;
INTCON2bits.RBPU = 0;  // enable PORTB internal pullups
INTCONbits.GIEL  = 0;
INTCON2bits.INTEDG1 = 0;
INTCON3bits.INT1IP = 0;
INTCON3bits.INT1IE = 1;
INTCON3bits.INT1IF = 0;
RCONbits.IPEN = 1;

WPUBbits.WPUB0 = 1;   // enable pull up on RB0

  while (1){PORTD=0xFF;Nop();Nop();PORTD=0x00;}

}

Not sure why you wish to see my circuit as I am using the internal oscillator, however its no different to the original demo board for the PIC18F45K20-I/MLPIC18F45K20-I/ML except for the addition of a Dallas DS1803E-010DS1803E-010 digital potentiometer wired into the I2C.

I program using an ICD3 with interface adaptor to 6 pin header.

The circuit should be fine, maybe I need a decoupling cap close to the DS1803E-010DS1803E-010 come to think of it, I am planning to use internal pullups on the I2C interface, but hey all I wanna know is how do you set up a PIC18F45K20-I/MLPIC18F45K20-I/ML to run code at max speed and give me a result I can see on a scope, answer in C18 please

I'm new here, thought I would chime in..

You will NOT see the full 64MHz (or even 16MHz) on a scope, if you're just looking at a pin output.

Assuming your uC is running at the full 64MHz (16MHz with 4X PLL and NO cpu division, aka CPU_DIV = 1), the instruction clock speed is actually 64MHz/4 = 16MHz, since the PIC18F architecture uses a "1 instruction per 4 clock cycle" division.

Then, your while loop is adding further overhead to your square wave output, because you are executing two instructions plus an additional comparison instruction or two per iteration of the while loop. That kills the frequency you would see on the output, and thus it is not representative of the true operating speed of the PIC. For a better (although still not ideal) test, simply copy the instructions "PORTD=0xFF;PORTD=0x00;" many many times in your main loop (or in a while(1) loop) and now try viewing the output on a scope. You should see a 16MHz/2 = 8MHz square wave, with an occasional hiccup (where the while loop ends/restarts). If you don't see around 8MHz something else is wrong, and if you're using the internal oscillator it almost HAS to be the software configuration of the oscillator bits or PLL. Hope that helps!

Thanks Brennathi, that is the answer that wins for me, makes perfect sense, hope I get the 8MHz squarewave when I try later

John

The best way to check the processor speed by toggling a port is to use a timer interrupt.

If you write code in C it will generate several assembly instructions and therefore you'll never toggle the port at the fastest speed. This is only possible in assembler.

Another VERY IMPORTANT point : for all ports bits that you use in output mode use LATx instead of PORTx.  e.g : LATD = 0xFF instead of PORTD = 0xFF.

If you use TIMER1 to generate interrupts with the prescaler set to 1/8 and writing (65536-20000) into PR1 you will generate an interrupt every Fosc/4  / 8 / 20000 = 10ms which will be easy to look at with a scope (or counting every 50 interrupts) with give a 1s blinking LED.

Note : assume Fosc = 64MHz

regards

But if you use an interrupt doesn't the PIC first have to jump to the interrupt vector, then jump to the service routine and THEN toggle the output pin? It seems like there would be just as much overhead that way. Or is there a way to directly toggle a pin the instant an interrupt is triggered?

The way I said will still work, even though it's not the most elegant solution. The C18 compiler will optimize the port toggle instructions so that they each only take one assembly instruction. You could also just directly toggle the port in assembly if you're paranoid about the compiler.

Thanks, can I mix assembler and C code together in the same project, how do I call assembler codes from my C program?.

Hi,

Yes, you can mix. I don't know which compiler do you use. But in MikroC it is done as simple as below,

asm bcf PORTB , 3

Firat