Revision as of 13:52, 18 March 2015

Amruta (talk) 13:28, 17 March 2015 (IST)

Basics

LPC1768 has 12 bit ADC which is multiplexed among 8 input pins. It's measurement range is typically 3V which means that ADC resolution is approximately 0.7 mV.

Registers

Here we will discuss commonly used ADC registers.

ADCR ( ADC Control Register )

ADCR
31:28	27	26:24	23:22	21	20:17	16	15:8	7:0
Reserved	EDGE	START	Reserved	PDN	Reserved	BURST	CLCKDIV	SEL

Bit 7:0 – SEL : Channel Select

These bits select which of the AD0.7:0 pins is (are) to be sampled and converted. There is one bit per channel e. g. bit o for AD0, bit 7 AD7.

Write one to enable respective channel. All zeroes is equivalent to 0x01.

Bit 15:8 – CLCKDIV : Clock Divisor

The APB clock (PCLK_ADC0) is divided by (this value plus one) to produce the clock for the A/D converter, which should be less than or equal to 13 MHz.

Bit 16 – BURST

Repeated conversions can be terminated by clearing this bit.

Bit 21 – PDN : Power Down Mode

Setting this bit brings ADC out of power down mode and makes it operational.

Bit 24:26 – START

When the BURST bit is 0, these bits control whether and when an A/D conversion is started:

Bit Value	FIFO Status
000	No Start
001	Start Conversion Now

The remaining cases (010 to 111) are about starting conversion on occurrence of edge on a particular CAP or MAT pin.

Bit 27 - EDGE

This bit is significant only when the START field contains 010-111. It starts conversion on selected CAP or MAT input.

Bit Value	Start Conversion
0	On Falling Edge
1	On Rising Edge

ADGDR ( ADC Global Data Register )

ADCR
31	27	26:24	23:16	15:4	3:0
Done	EDGE	Channel	Reserved	RESULT	Reserved

Schematic

Code

/*-----------------------------------------------------------------------------
note : Refer adc.h to enable ADC channels.
------------------------------------------------------------------------------*/
#include "lpc17xx.h"	//device specific heaader file
#include "uart.h"		//Explore Embedded UART library which conatins the lcd routines
#include "adc.h"		//Explore Embedded ADC library which conatins the adc routines
 
/* start the main program */
int main() 
{
   uint16_t adc_result;
 
  /* Setup and initialize the microcontroller system */
	SystemInit();
 
  /* Initialize the UART before displaying any thing on the lcd */
	UART_Init(UART0,9600);
 
  /* Initialize the adc before starting the conversion */
	ADC_Init();
 
  /* Display "ADC Channel zero" on first line*/
	UART_Printf("ADC Channel zero");
 
   /* Display the adc channel zero value continously */ 
   while(1)
    {
		/*Get the adc value of channel five */
		adc_result= ADC_GetAdcValue(5);
 
		/*Display the adc value on UART*/
		UART_Printf("\n %u",adc_result);
	}
}

@@ Line 41: / Line 41: @@
 !Bit Value || FIFO Status
 |-
-|0|| Empty
+|000|| No Start
 |-
-|1|| Not Empty
+|001|| Start Conversion Now
+|}
+The remaining cases (010 to 111) are about starting conversion on occurrence of  edge on a particular CAP or MAT pin.
+'''Bit 27 - EDGE'''
+This bit is significant only when the START field contains 010-111.
+It starts conversion on selected CAP or MAT input.
+{| class="wikitable" style="text-align:center; background-color:#C0C0C0;"
+!Bit Value || Start Conversion
+|-
+|0|| On Falling Edge
+|-
+|1||On Rising Edge
 |-
 |}

Difference between revisions of "ARM ADC Programming"