first init

avr_adc.c

@@ -0,0 +1,52 @@
+//setup adc for an attiny85
+//
+#include<avr/io.h>
+#include"avr_adc.h"
+#define _BS(bit) (1<<bit)
+#define _BC(bit) ~(1<<bit)
+#define STARTADC ADCSRA |= _BS(ADSC)
+
+
+		//1.setup_prescaler
+		  /* this function initialises the ADC
+
+        ADC Prescaler Notes:
+	--------------------
+
+	   ADC Prescaler needs to be set so that the ADC input frequency is between 50 - 200kHz.
+
+           For more information, see table 17.5 "ADC Prescaler Selections" in
+           chapter 17.13.2 "ADCSRA – ADC Control and Status Register A"
+          (pages 140 and 141 on the complete ATtiny25/45/85 datasheet, Rev. 2586M–AVR–07/10)
+
+           Valid prescaler values for various clock speeds
+
+	     Clock   Available prescaler values
+           ---------------------------------------
+             1 MHz   8 (125kHz), 16 (62.5kHz)
+             4 MHz   32 (125kHz), 64 (62.5kHz)
+             8 MHz   64 (125kHz), 128 (62.5kHz)
+            16 MHz   128 (125kHz)
+
+           Below example set prescaler to 128 for mcu running at 8MHz
+           (check the datasheet for the proper bit values to set the prescaler)
+  */
+void setupADC(void)
+{
+		ADMUX = //_BC(REFS0) |	//Set_Vref 
+				//_BC(REFS1) |	//Set_Vref
+				//_BC(MUX3)  |	//
+				//_BC(MUX2)  |	//
+				_BS(MUX1)  |	//
+				_BS(MUX0)  |	//PORT Select PB3
+				_BS(ADLAR) ;		//left shift conversion results(used in 8bit mode)
+
+		ADCSRA = _BS(ADEN) |	//Enable ADC
+				//_BC(ADATE) |	//Disable AutoTrigger aka Freerunning mode
+				_BS(ADPS2) |	//Select Prescaler	clk/32
+				//_BC(ADPS1) |
+				_BS(ADPS0);
+
+}
+
+