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Advanced Processors - TE
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Savitribai Phule Pune University
Electronics and Telecommunication Engineering
Third Year
Advanced Processors - TE
Unit 4 : Real World Interfacing with ARM7 Based Microcontroller -2
DAC in LPC2148
DAC in LPC2148
DAC in LPC2148
Features of DAC
LPC2148 has one 10-bit DAC
Settling time software selectable
DAC output can drive max of 700 micro-Ampere or 350 micro-Ampere
DAC peripheral has only one register, DACR
It contains 10-bit value for conversion in bit[15:6] position
Bit[16] selects settling time, ‘1’ selects 1 micro-seconds settling time and 700 micro-Ampere Current
'0’ selects 2.5 micro-seconds settling time and 700 micro-Ampere Current
DAC Pin Description
Pin Type Description
AOUT Output Analog Output. After the selected settling time after the DACR is written with a new value, the voltage on this pin (with respect to VSSA) is VALUE/1024 * VREF.
VREF Reference Voltage Reference. This pin provides a voltage reference level for the D/A converter.
VDDA, VSSA Power Analog Power and Ground. These should be nominally the same voltages as V3 and VSSD, but should be isolated to minimize noise and error.
Digital to Analog Control Register (DACR)
31-17 16 15-6 5-0
Reserved BIAS 10-bit Digital Value Reserved
DAC Register (DACR - address OxE006 C000) Bit Description
Bit Symbol Value Description Reset value
5:0 - Reserved, user software should not write ones to reserved NA bits. The value read from a reserved bit is not defined. NA
15:6 VALUE After the selected settling time after this field is written with a 0 new VALUE, the voltage on the AOUT pin (with respect to VssA) is VALUE/1024 * VREF. 0
16 BIAS 0 The settling time of the DAC is 1 µs max, and the maximum current is 700 µA. 0
1 The settling time of the DAC is 2.5 µs and the maximum current is 350 µA.
31:17 - Reserved, user software should not write ones to reserved NA bits. The value read from a reserved bit is not defined. NA
Example:
Configure DAC register for generating with 3.3V VREF & Select 350 microAMPERE settling time.
0V,
1.65V,
3.3V
Formula:
AOUT= VREF * (10 bit Digital Value/Resolution)
Solution:
DACR = 0x00010000; //AOUT = 0V
DACR = 0x00018000; //AOUT = 1.65V
DACR = 0x0001FFC0; //AOUT = 3.3 V
Draw DAC interfacing diagram with LPC2148. Also write program for triangular waveform generation
Interfacing Diagram
dac interfacing
Configuring internal DAC of LPC2148 for Generation of Triangular waveform
Embedded C Program for Sine Waveform Generation
/**************************************************************************/
/* Project Name:- Sine waveform generation using internal DAC of LPC2148 */
/* Device:- LPC2148 */
/* Compiler:- KeilUvision4 */
/* Language:- Embedded C*/
/* Visit www.wikinote.org for more Details */
/********************************************************************************************/
#include <lpc214x.h>
#include <stdint.h>
void delay_ms(uint16_t j)
{
uint16_t x,i;
for(i=0;i<j;i++)
{
for(x=0; x<6000; x++); /* loop to generate 1 milisecond delay with Cclk = 60MHz */
}
}
int main (void)
{
uint16_t value;
uint8_t i;
i = 0;
PINSEL1 = 0x00080000; /* P0.25 as DAC output */
uint16_t sin_wave[42] = { 512,591,665,742,808,873,926,968,998,1017,1023,1017,998,968,926,873,808,742,665,591,512,
436,359,282,216,211,151,97,55,25,6,0,6,25,55,97,151,211,216,282,359,436 };
while(1)
{
while(i !=42)
{
value = sin_wave[i];
DACR = ( (1<<16) | (value<<6) );///Bias bit=1, Digital Value left shifted by 6 bits
delay_ms(1);
i++;
}
i = 0;
}
}
Embedded C code for Triangular Waveform Generation
/**************************************************************************/
/* Project Name:- Triangular wave generation using internal DAC of LPC2148 */
/* Device:- LPC2148 */
/* Compiler:- KeilUvision4 */
/* Language:- Embedded C*/
/* Visit www.wikinote.org for more Details */
/********************************************************************************************/
#include <lpc214x.h>
#include <stdint.h>
void delay_ms(uint16_t j)
{
uint16_t x,i;
for(i=0;i<j;i++)
{
for(x=0; x<6000; x++); /* loop to generate 1 milisecond delay with Cclk = 60MHz */
}
}
int main (void)
{
uint16_t value;
uint8_t i;
i = 0;
PINSEL1 = 0x00080000; /* P0.25 as DAC output */
while(1)
{
value = 0;
while ( value != 1023 )
{
DACR = ( (1<<16) | (value<<6) );
value++;
}
while ( value != 0 )
{
DACR = ( (1<<16) | (value<<6) );
value--;
}
}
}
Embedded C Program for Square Waveform Generation
/**************************************************************************/
/* Project Name:- Square waveform generation using internal DAC of LPC2148 */
/* Device:- LPC2148 */
/* Compiler:- KeiluVision4 */
/* Language:- Embedded C */
/* Visit www.wikinote.org for more Details */
/********************************************************************************************/
#include <lpc214x.h>
#include <stdint.h>
void delay_ms(uint16_t j)
{
uint16_t x,i;
for(i=0;i<j;i++)
{
for(x=0; x<6000; x++); /* loop to generate 1 milisecond delay with Cclk = 60MHz */
}
}
int main (void)
{
uint16_t value;
uint8_t i;
i = 0;
PINSEL1 = 0x00080000; /* P0.25 as DAC output */
while(1)
{
value = 1023;
DACR = ( (1<<16) | (value<<6) );
delay_ms(100);
value = 0;
DACR = ( (1<<16) | (value<<6) );
delay_ms(100);
}
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