| ??? 06/05/10 16:14 Modified: 06/05/10 16:18 Read: times |
#176430 - T0 overflows at 65535+1, don't overlook this Responding to: ???'s previous message |
Murray R. Van Luyn said:
// In your module's associated header file... #define CRYSTAL_FREQ 11059200 #define STATES_PER_CYCLE 12u #define PERIPH_CLOCK_FREQ CRYSTAL_FREQ / STATES_PER_CYCLE #define OSC_FREQUENCY 8000u #define PERIOD_COUNTS PERIPH_CLOCK_FREQ / OSC_FREQUENCY #define T0_OVERFLOW 65535u #define RELOAD (unsigned int)(T0_OVERFLOW - PERIOD_COUNTS) // In your timer initialisation routine... TL0 = (unsigned char)(RELOAD & 0xFF); TH0 = (unsigned char)(RELOAD >> 8); The calculation above looks nice but misses that Timer T0 overflows at 65535+1 = 65536 and an unsigned int type cannot hold that value. The overlooked value 65535u used in the calculations above should be corrected by +1 as shown below: #define T0_OVERFLOW 65535u #define RELOAD (unsigned int)(T0_OVERFLOW - PERIOD_COUNTS + 1) Also because of rounding due to the integer division, the calculation of RELOAD is out by +/- 1 that means a deviation error for the result of relative small values. A better way is to do such calculations on a dedicated spreadsheet for every project and then check the if the C pre-processor #define made the same result. K.L.Angelis |
| Topic | Author | Date |
| 80C52 Timer0 | 01/01/70 00:00 | |
| where is the EA initialize? | 01/01/70 00:00 | |
| EA initialize | 01/01/70 00:00 | |
| no reason in what you show | 01/01/70 00:00 | |
| TL0 and TH0 | 01/01/70 00:00 | |
| Calculations for Timer T0 at 8KHz: have you tried 0xFF8D ??? | 01/01/70 00:00 | |
| correction | 01/01/70 00:00 | |
| Yeah - 0x8D | 01/01/70 00:00 | |
| Thanks for that typo, More for 8KHz with 50% duty cycle | 01/01/70 00:00 | |
| Put the compiler to work... | 01/01/70 00:00 | |
| fine, but | 01/01/70 00:00 | |
| T0 overflows at 65535+1, don't overlook this | 01/01/70 00:00 | |
| right answer, wrong premise | 01/01/70 00:00 | |
| Exact calculations require semantics | 01/01/70 00:00 | |
| you are welcome to find out | 01/01/70 00:00 | |
Thanks for the correction... | 01/01/70 00:00 |