blob: ef5e62232a8f15760d0f44e415fc4606ac1bd1e9 (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
|
#include <pic16f84a.h>
typedef unsigned char uint8_t;
__sfr __at(0x70) UART_TX;
__sfr __at(0x72) UART_STATUS;
/*
* OPTION_REG 0x07: T0CS=0 (Fosc/4), PSA=0, PS=111 (1:256)
* At 50 MHz: overflow every 256*256 / (50M/4) = 5.24 ms → ~191 ovf/sec
*/
#define STATUS_RP0 0x20
#define T0IF 0x04 /* INTCON bit 2 */
#define T0IE 0x20 /* INTCON bit 5 */
#define GIE 0x80 /* INTCON bit 7 */
#define OVF_PER_SEC 191
static volatile uint8_t ovf_count = 0;
void isr(void) __interrupt(0) {
if (INTCON & T0IF) {
ovf_count++;
INTCON &= ~T0IF;
}
}
static void uart_send(uint8_t b) {
while (UART_STATUS & 0x01);
UART_TX = b;
}
static void uart_puts(const char *s) {
while (*s) uart_send((uint8_t)*s++);
}
static void print_uint8(uint8_t v) {
uint8_t started = 0;
if (v >= 200) { uart_send('2'); v -= 200; started = 1; }
else if (v >= 100) { uart_send('1'); v -= 100; started = 1; }
{
uint8_t t = '0';
while (v >= 10) { v -= 10; t++; }
if (started || t != '0') uart_send(t);
}
uart_send(v + '0');
}
void main(void) {
uint8_t seconds = 0;
/* Configure OPTION_REG (bank 1, same 7-bit addr as TMR0) */
STATUS |= STATUS_RP0;
TMR0 = 0x07;
STATUS &= ~STATUS_RP0;
TMR0 = 0;
INTCON = T0IE | GIE; /* enable Timer0 overflow interrupt */
uart_puts("\x1B[2J\x1B[H");
uart_puts("Timer0 test\r\n");
uart_puts("-----------\r\n");
while (1) {
ovf_count = 0;
while (ovf_count < OVF_PER_SEC); /* ISR bumps ovf_count */
uart_puts("t = ");
print_uint8(seconds);
uart_puts(" s\r\n");
PORTA ^= 0x01;
seconds++;
}
}
|
