pic_therm

PIC16F877A and BME280 thermometer
git clone git://git.margiolis.net/pic_therm.git
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tmr0.h (807B)


      1 #ifndef _TMR0_H_
      2 #define _TMR0_H_
      3 
      4 #include "extern.h"
      5 
      6 #define TMR0_CLK0 (0 << 5)		/* Use the CLK0 pin */
      7 /*
      8  * Bit 3 assigns the prescalar to TMR0.
      9  * Bits 0-2 of OPTION_REG indicate the prescalar value. In this case,
     10  * 111 indicates a prescalar value of 256.
     11  */
     12 #define TMR0_PRESCALAR_256 0b0111
     13 /* 
     14  * We want 1ms delay @ 16Mhz with 64 prescalar, the formula is:
     15  *
     16  * 256 - ((delay * (fosc / 1000)) / (prescalar * 4)) =
     17  * 256 - ((1 * (16000000 / 1000)) / (256 * 4)) =
     18  * 256 - ((1 * 16000) / (256 * 4)) = ~240
     19  *
     20  * sdcc thinks there's an overflow here (hint: he's wrong)...
     21  */
     22 #define TMR0_DELAY (256 - ((1 * (_XTAL_FREQ / 1000)) / (256 * 4)))
     23 
     24 typedef void (*ev_handler)(void);
     25 
     26 void	tmr0_init(void);
     27 void	tmr0_delay_ms(uint16_t);
     28 int	tmr0_set_event(ev_handler, uint16_t);
     29 
     30 #endif /* _TMR0_H_ */