18f27k40 - timer0 changes from K22, K80 series 8bit/16bit mode

[richard]

@ fosc=16mhz settings from mcc for a 10mS timer
pic18f25k22

 // Set TMR0 to the options selected in the User Interface
    // TMR0H 0; 
    TMR0H = 0x00;
    // TMR0L 100; 
    TMR0L = 0x64;
 
    // Load TMR0 value to the 8-bit reload variable
    timer0ReloadVal = 100;
    // Clearing IF flag
    INTCONbits.TMR0IF = 0;
    // T0PS 1:256; T08BIT 8-bit; T0SE Increment_hi_lo; T0CS FOSC/4; TMR0ON enabled; PSA assigned; 
    T0CON = 0xD7;

18f27k40

       // Set TMR0 to the options selected in the User Interface

    // T0CS FOSC/4; T0CKPS 1:64; T0ASYNC synchronised; 
    T0CON1 = 0x46;

    // TMR0H 155; 
    TMR0H = 0x9B;

    // TMR0L 0; 
    TMR0L = 0x00;

    // Clearing IF flag
    PIR0bits.TMR0IF = 0;

    // T0OUTPS 1:1; T0EN enabled; T016BIT 8-bit; 
    T0CON0 = 0x80;

[longpole001]

thanks guys

i am running at 32mhz , so a few changes , its nice have both the prescaller and the postscaller something that timer0 never had , and without it 10ms in 8bit mode functioning in same way as TMR2 would not be possible at 32mhz

i pointed this out cos i have ported timer0 code from one processor to another , and was not expecting a change in timer0 internal functions when in 8 bit mode

cheers

Sheldon

[longpole001]

oh and when i first setup this original code, back some years back i refereed to this calculator, so dont use this calc for timer 0 for k40

[tumbleweed]

// T0CS FOSC/4; T0CKPS 1:64; T0ASYNC synchronised;
// TMR0H 155;
// TMR0L 0;
// T0OUTPS 1:1; T0EN enabled; T016BIT 8-bit;

For the K40 in 8-bit mode I don't see how that gets you 10ms @ 16MHz clock

Doesn't that get you 156 x 64 x 250ns = 2.496ms ?

[richard]

Doesn't that get you 156 x 64 x 250ns = 2.496ms ?

yes , my bad it needs to be T0CKPS 1:256;

accidently set fosc to 4mhz when trying to match sheldons settings trying to guess at his fosc and forgot to regenerate the code

[tumbleweed]

it needs to be T0CKPS 1:256

That'll get you a lot closer... 9.984ms

If you use the postscaler you can get 10.000ms:

- set prescaler to 1:32 T0CKPS<3:0> = 0101
- set postscaler to 1:10 T0OUTPS<3:0> = 1001
- set period count = 125 (load TMR0H with 125-1=124)
gets you 32 x 10 x 125 x 250ns = 10.000ms

For 32MHz, just change the prescaler to 1:64:
64 x 10 x 125 x 125ns = 10.000ms

[richard]

i'm impressed on just how versatile these later generation chips are. there is heaps to learn