Quick questions about timer

[bananasiong]

Hi,
I have some quick questions about timer:

1. When watchdog timer overflows, the PIC will reset, so it goes to org 0x0000 or somewhere else desired by the user? I think it will be at 0x0000 because it resets, just to confirm.

2. A timer (either 0, 1, 2 or 3) will keep running from 0 to full then back to 0 again without doing any setting in the program? For example, I need a random 8 bit number, so I simply take the value of tmr0 in anywhere of the program will do?

Thanks

 

[Pommie]

1. Yes, the pic will reset. You can check the value of various bits to establish if it was a WDT reset. Refer to table 12-2 in the 16f88 data sheet.

2. Yes, however the values you get will not be very random. If you wait for a key press or some other external trigger then the value will be pretty random. Which pic has timer 3?

Mike.

 

[blueroomelectronics]

1. Yes, the pic will reset. You can check the value of various bits to establish if it was a WDT reset. Refer to table 12-2 in the 16f88 data sheet.

2. Yes, however the values you get will not be very random. If you wait for a key press or some other external trigger then the value will be pretty random. Which pic has timer 3?

Mike.

Why the 18F and above often have timer 3

 

[bananasiong]

Yes, thanks
But you mean that the value will not be very random because the timer increase one for every instruction cycle; if I get the value of tmr0 in very begging of the program, I will properly get small value, am I right?
And yes, I've seen timer 3 in 18f series, but I have not started touching them because I'm still in the process of learning the 16f series

 

[eng1]

Hi,
1. When watchdog timer overflows, the PIC will reset, so it goes to org 0x0000 or somewhere else desired by the user? I think it will be at 0x0000 because it resets, just to confirm.

Except when the PIC is sleeping. In that case a WatchDog Timer time-out causes the PIC to wake up and continue executing the code after the SLEEP instruction.

if I get the value of tmr0 in very begging of the program, I will properly get small value, am I right?

You'll very likely get the same number every time

I've used TMR2 running as fast as possible to generate random numbers. The trick was to read the value of TMR2 when a button was pressed. If you don't have external events, consider specific routines like - if it's worth trying for you application.

 

[bananasiong]

Yes, I agree that the same value will be got in this case.
The loop of getting the value of tmr0 in my program is not called all the time, so I can get random number when I call the loop.

 

[bananasiong]

Hi,
Do I need to do anything to reset TMR0 when it overflows? I got 0xff all the time when I tried to read from it. I read the value of TMR0 when a button is pressed, so I think I can get 8 bit random number, but couldn't.

Thanks

 

[bananasiong]

Oh god, I found it. I forgot to clear the T0CS bit of the OPTION_REG. The default setting of this bit is 1. Now I can get random numbers

 

[donniedj]

This was just Timer0 and will be more nitpiky once you use the other timers.

INTCON
OPTION_REG
PIR
PIE
T1CON
T2CON

I start a project with a full template similar to the partially full one below. Once I reach the point of near completion, I tiddy up by remove all uneccessary Defaults in the Start section and set bits and flag by Masking a byte as opposed to bcf/bsf each individual bit.

START:	;-----PORT I/O CONFIGURATION-------------------------------
        NOP
        BANK1
	BSF	CMCON0, CM2		;DISABLE COMPARATOR.
	BSF	CMCON0, CM1		
	BSF	CMCON0, CM0
	BANK1
        LOADF    TRISA, B'11011111'
        LOADF    TRISB, B'00000000'
	LOADF	TRISC, B'00000000'
        BSF	OPTION_REG, NOT_RBPU	;BCF/BSF = ENABLE/DISABLE PULL-UP.
	BCF	OPTION_REG, INTEDG 	;BSF/BCF = HIGH/LOW - RB0/INT EDGE TRIGGER
	BANK2
	CLRF	LCDCON
	BANK1	;------POWER ON RESET CONFIGURATION--------------------------
	BSF	OSCCON, IRCF2	;INTERNAL OSCILLATOR FREQUENCY.
	BSF	OSCCON, IRCF1	;110=4MHZ	
	BCF	OSCCON, IRCF0
	BSF	OSCCON, SCS	;C/S = INTERNAL/FOSC  SYSTEM CLOCK
	BANK1	;------ANALOG CONFIGURATION----------------------------------
	BCF	ANSEL, ANS4	;C/S=DIGITAL/ANALOG PIN
	BCF	ANSEL, ANS3	;C/S=DIGITAL/ANALOG PIN
	BCF	ANSEL, ANS2	;C/S=DIGITAL/ANALOG PIN
	BCF	ANSEL, ANS1	;C/S=DIGITAL/ANALOG PIN
	BCF	ANSEL, ANS0	;C/S=DIGITAL/ANALOG PIN
	BANK1	;------INTERRUPT CONFIGURATION-------------------------------
	BSF	INTCON, PEIE	;C/S=DIS/ENABLE    PERIPHERAL INTERRUPTS
	BSF	PIE1, TMR1IE  	;C/S=DIS/ENABLE    TIMER1     INTERRUPT
	BCF	PIE1, CCP1IE	;C/S=DIS/ENABLE	   CAPTURE    INTERRUPT
	BCF	PIE2, C2IE	;C/S=DIS/ENABLE	   COMPARATOR INTERRUPT
	BCF	PIE1, EEIE	;C/S=DIS/ENABLE	   EEPROM     INTERRUPT
	BSF	INTCON, GIE  	;C/S=DIS/ENABLE    GLOBAL     INTERRUPT
	BCF	INTCON, T0IE	;C/S=DIS/ENABLE    TIMER0     INTERRUPT
        BANK0	;----TIMER1 CONFIGURATION-----------------------------------
	BSF	T1CON, TMR1ON 	;C/S=DIS/ENABLE     	      TIMER1 ON
	BCF	T1CON, TMR1CS 	;C/S=IN/EXTERNAL(RA6)    	  CLOCK
        BANK1	;----TIMER0 CONFIGURATION-----------------------------------
	BCF	OPTION_REG, T0CS	;C/S=IN/EXTERNAL(RA4)   	       CLOCK
	BCF	OPTION_REG, PSA	;C/S=TIMER0/WDT    PRESCALER ASSIGNMENT
	BSF	OPTION_REG, .2	;PRESCALER
	BSF	OPTION_REG, .1	;000=1:2,  001=1:4,  010=1:8,   011=1:16
	BSF	OPTION_REG, .0	;100=1:32, 101=1:64, 110=1:128, 111=1:256
	BANK1	;----SERIAL TRANSMIT CONFIGURATION------------------------
	BSF	TXSTA, TXEN	;C/S=DIS/ENABLE             TRANSMISSION
	BSF	TXSTA, BRGH	;C/S=LO/HI SPEED        BAUD RATE SELECT
	LOADF	SPBRG, .10	;BAUD RATE: 21= 57.6K BPS  10=115.2 KBPS
	BANK0	;----SERIAL RECEIVE CONFIGURATION-------------------------
	BSF	RCSTA, SPEN	;C/S=DIS/ENABLE              SERIAL PORT
	BSF	RCSTA, SREN	;C/S=DIS/ENABLE           SINGLE RECEIVE	
	BSF	RCSTA, CREN	;C/S=DIS/ENABLE        CONTINUOS RECEIVE
 	BANK0	;---------------------------------------------------------

I still keep a copy of the pdf bible running in the background, alt-tabbing, ctrl-F'ing, and F3'ing like a made man.