BSRAM progmem. fix Makefile memory command that does not work. add interrupts, bank 1, timer0. Timer0 not tested.

1 files changed, 156 insertions, 0 deletions

diff --git a/fw/ds18b20.c b/fw/ds18b20.c
new file mode 100644
index 0000000..0b57732
--- /dev/null
+++ b/fw/ds18b20.c
@@ -0,0 +1,156 @@
+#include <pic16f84a.h>
+
+typedef unsigned char uint8_t;
+
+__sfr __at(0x70) UART_TX;
+__sfr __at(0x72) UART_STATUS;
+
+__sfr __at(0x73) OW_DATA;
+__sfr __at(0x74) OW_CMD;
+__sfr __at(0x75) OW_STATUS;
+
+#define OW_RESET     0x00
+#define OW_WRITE     0x01
+#define OW_READ      0x02
+
+#define OW_BUSY      0x01
+#define OW_PRESENCE  0x02
+
+#define CMD_SKIP_ROM     0xCC
+#define CMD_CONVERT_T    0x44
+#define CMD_READ_SCRATCH 0xBE
+
+/*
+ * Fractional nibble lookup: each step is 0.0625 deg C.
+ * Tables give the two decimal digits (tenths, hundredths) truncated.
+ * e.g. frac=1 -> 0.0625 -> prints ".06"
+ *      frac=8 -> 0.5000 -> prints ".50"
+ */
+static const uint8_t frac_tens[16] = {0,0,1,1,2,3,3,4,5,5,6,6,7,8,8,9};
+static const uint8_t frac_hund[16] = {0,6,2,8,5,1,7,4,0,6,2,8,5,1,7,3};
+
+/*
+ * Timer0 delay.  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.
+ * 143 overflows ≈ 750 ms.
+ */
+#define STATUS_RP0    0x20
+#define T0IF          0x04
+
+static void wait_overflows(uint8_t n) {
+    INTCON &= ~T0IF;
+    while (n--) {
+        while (!(INTCON & T0IF));
+        INTCON &= ~T0IF;
+    }
+}
+
+static void delay_750ms(void) { wait_overflows(143); }
+
+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 ow_wait(void) {
+    while (OW_STATUS & OW_BUSY);
+}
+
+static void ow_write_byte(uint8_t b) {
+    OW_DATA = b;
+    OW_CMD  = OW_WRITE;
+    ow_wait();
+}
+
+static uint8_t ow_read_byte(void) {
+    OW_CMD = OW_READ;
+    ow_wait();
+    return OW_DATA;
+}
+
+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 lo, hi, sign, temp_int, frac;
+    uint8_t i;
+
+    /* Configure Timer0: bank 1, OPTION_REG = 0x07 (Fosc/4, prescaler 1:256) */
+    STATUS |= STATUS_RP0;
+    TMR0 = 0x07;
+    STATUS &= ~STATUS_RP0;
+
+    uart_puts("\x1B[2J\x1B[H");
+    uart_puts("DS18B20 Temperature\r\n");
+    uart_puts("-------------------\r\n");
+
+    while (1) {
+        /* Reset */
+        OW_CMD = OW_RESET;
+        ow_wait();
+        if (!(OW_STATUS & OW_PRESENCE)) {
+            uart_puts("No sensor\r\n");
+            delay_750ms();
+            continue;
+        }
+
+        /* Start temperature conversion */
+        ow_write_byte(CMD_SKIP_ROM);
+        ow_write_byte(CMD_CONVERT_T);
+        delay_750ms();
+
+        /* Reset and read scratchpad */
+        OW_CMD = OW_RESET;
+        ow_wait();
+        if (!(OW_STATUS & OW_PRESENCE)) {
+            uart_puts("Lost sensor\r\n");
+            continue;
+        }
+        ow_write_byte(CMD_SKIP_ROM);
+        ow_write_byte(CMD_READ_SCRATCH);
+
+        lo = ow_read_byte();   /* scratchpad byte 0: temp LSB */
+        hi = ow_read_byte();   /* scratchpad byte 1: temp MSB */
+        for (i = 0; i < 7; i++) ow_read_byte();  /* discard remaining bytes */
+
+        /*
+         * DS18B20 12-bit format:
+         *   sign = hi bit 7 (and sign-extended through hi[7:4])
+         *   integer part = hi[3:0]:lo[7:4]
+         *   fractional nibble = lo[3:0]  (each bit = 0.0625 deg C)
+         *
+         * Negative values are two's complement of the 16-bit word.
+         */
+        sign = hi & 0x80;
+        if (sign) {
+            lo = ~lo;
+            hi = ~hi;
+            if (lo == 0xFF) { lo = 0; hi++; }
+            else             { lo++;       }
+        }
+
+        temp_int = ((hi & 0x0F) << 4) | (lo >> 4);
+        frac     = lo & 0x0F;
+
+        uart_puts("\rTemp: ");
+        if (sign) uart_send('-');
+        print_uint8(temp_int);
+        uart_send('.');
+        uart_send('0' + frac_tens[frac]);
+        uart_send('0' + frac_hund[frac]);
+        uart_puts(" C\r\n");
+    }
+}