Revision 0:d0b35e0b4294, committed 2009-11-18

Comitter:

simon

Date:

Wed Nov 18 09:26:15 2009 +0000

Commit message:

Changed in this revision

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Wed Nov 18 09:26:15 2009 +0000
@@ -0,0 +1,97 @@
+#include "mbed.h"
+
+// DS18B20 converted to run on mbed
+
+#define TEMP_PIN  p20
+
+Serial pc(USBTX, USBRX); // tx, rx
+
+DigitalInOut temperature_pin(TEMP_PIN);
+
+void OneWireReset() { // reset.  Should improve to act as a presence pulse
+    temperature_pin.output();
+    temperature_pin = 0;     // bring low for 500 us
+    wait_us(500);
+    temperature_pin.input();
+    wait_us(500);
+}
+
+void OneWireOutByte(unsigned char d) { // output byte d (least sig bit first).
+    for(int n=8; n!=0; n--) {
+        if ((d & 0x01) == 1) { // test least sig bit
+            temperature_pin.output();
+            temperature_pin = 0;
+            wait_us(5);
+            temperature_pin.input();
+            wait_us(60);
+        } else {
+            temperature_pin.output();
+            temperature_pin = 0;
+            wait_us(60);
+            temperature_pin.input();
+        }
+
+        d=d>>1; // now the next bit is in the least sig bit position.
+    }
+
+}
+
+unsigned char OneWireInByte() { // read byte, least sig byte first
+    unsigned char d = 0, b;
+    for (int n=0; n<8; n++) {
+        temperature_pin.output();
+        temperature_pin = 0;
+        wait_us(5);
+        temperature_pin.input();
+        wait_us(5);
+        b = temperature_pin;
+        wait_us(50);
+        d = (d >> 1) | (b << 7); // shift d to right and insert b in most sig bit position
+    }
+    return d;
+}
+
+int main() {
+    int HighByte, LowByte, TReading, SignBit, Tc_100, Whole, Fract;
+    pc.printf("mbed 1 wire interface simple test!\r\n");
+    temperature_pin.output();
+    temperature_pin = 0;
+    temperature_pin.input();  // sets the digital pin as input (logic 1) make sure external pullup resistor 4K7
+    wait(1);
+    pc.printf("temperature measurements:\r\n");
+
+    while (1) {
+        OneWireReset();
+        OneWireOutByte( 0xcc);  //Skip ROM command
+        OneWireOutByte( 0x44); // perform temperature conversion, strong pullup for one sec
+
+        OneWireReset();
+        OneWireOutByte( 0xcc);
+        OneWireOutByte( 0xbe);   //Read Scratchpad
+
+        LowByte = OneWireInByte();
+        HighByte = OneWireInByte();
+        TReading = (HighByte << 8) + LowByte;
+        SignBit = TReading & 0x8000;  // test most sig bit
+        if (SignBit) { // negative
+            TReading = (TReading ^ 0xffff) + 1; // 2's comp
+        }
+        Tc_100 = (6 * TReading) + TReading / 4;    // multiply by (100 * 0.0625) or 6.25
+
+        Whole = Tc_100 / 100;  // separate off the whole and fractional portions
+        Fract = Tc_100 % 100;
+
+        if (SignBit) { // If its negative
+            pc.printf("-");
+        }
+        pc.printf("%d", Whole);
+        pc.printf(".");
+        if (Fract < 10) {
+            pc.printf("0");
+        }
+        pc.printf("%d", Fract);
+        pc.printf("\r\n");
+       
+        wait(5);         // 5 second delay.  Adjust as necessary
+    }
+}
\ No newline at end of file

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed.bld	Wed Nov 18 09:26:15 2009 +0000
@@ -0,0 +1,1 @@
+http://mbed.org/users/mbed_official/code/mbed/builds/32af5db564d4