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Markdem
Joined: 24 Jun 2005
Posts: 206
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| MCP3421 |
 Posted: Fri Feb 02, 2007 7:17 pm |
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Hi All, i am tring to write a driver for the new MCP3421 ADC.
I have connected it to a known working I2C bus, and am just tring to read the ADC result for now. I am tring the following code;
| Code: |
#include <18F4550.h>
#fuses HSPLL,NOWDT,NOPROTECT,NOLVP,NODEBUG,USBDIV,PLL5,CPUDIV1,VREGEN,NOBROWNOUT
#use delay(clock=48000000)
#use i2c(MASTER, SDA=PIN_B0, SCL=PIN_B1)
#include <HDM64GS12.c>
#include <graphics.c>
#define LCDBacklightOUT PIN_E0
char lcddata[30];
int byte0, byte1, byte2;
void main()
{
delay_ms(10);
output_high(lcdbacklightout);
glcd_init(ON);
sprintf(lcddata,"Ready");
glcd_text57(1,1,lcddata,1,on);
while(1)
{
i2c_start();
i2c_write(0xD1); //send address of MCP3421
delay_us(10);
byte0 = i2c_read(1); //read first byte and send ack
byte1 = i2c_read(1); //read second byte and send ack
byte2 = i2c_read(0); //read last byte and dont ack
i2c_stop();
sprintf(lcddata,"%u, %u, %u", byte0, byte1, byte2);
glcd_text57(1,10,lcddata,1,on);
delay_ms(1000);
glcd_rect(0, 10, 128, 20, no, off);
}
}
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All i get back formt he MCP3421 is all 1s. If I disconnect it, i will still get 1s. It looks like i am not talking to it, but i cant see why. I have read the datasheet meany time, but i cant work out what i am doing wrong.
Thanks,
Mark |
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kender
Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley
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| Posted: Fri Feb 02, 2007 8:44 pm |
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Are you getting 0xFFFFFF or 0x03FFFF (18 ones or 24 ones)?
What reading do you expect? At what potential are Vin(+) and Vin(-)? Table 4-2 in the datasheet says that all 1s corresponds to the input of -1 LSB. A tiny bias could cause that.
I2C could be miss-wired at MCP3421 itself. Can you talk to other I2C devices, while MCP3421 is still connected to the bus?
Wrong slave address. You could get a chip with an address other than default 0xD0, although it's unlikely.
Fried chip is the last on the list. |
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Markdem
Joined: 24 Jun 2005
Posts: 206
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| Posted: Fri Feb 02, 2007 9:50 pm |
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Thanks Kender, I am getting 0xFFFFFF, so 24 ones.
I have +1v accross the inputs, so i should not be getting all ones.
I can still read from a DS1307 clock, so i think the bus is OK.
Does the code look OK? Is there any timing issues that i am not thinking about?
Thanks, Mark |
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kender
Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley
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| Posted: Fri Feb 02, 2007 10:12 pm |
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The code looks fine. According to the fig 5-2 in the datasheet, you should be able to read the 3 value bytes back-to-back. Timing could be an issue. The datasheet says (5.5) that the high speed mode needs to be activated with a separate command. Try to reduce f_SCL to 100kHz. May be adding delays between the I2C bytes could help too.
By the way, is MCP3421 getting enough power? |
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Markdem
Joined: 24 Jun 2005
Posts: 206
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| Posted: Sat Feb 03, 2007 6:40 pm |
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OK, i have now added delays between the reads, but it did not help. I have checked that the MCP is getting 5v, and it is OK.
I am not tring to you high speed mode, but i have tried forcing the bus slow, but that also did nothing.
I wish i had a scope so i could check if the MCP is sending ack back 
I think i will try to change the MCP to see if it is maybe damaged.
Thanks
Mark |
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ohararp
Joined: 10 May 2009
Posts: 1
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| Posted: Sun May 10, 2009 2:15 pm |
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| Mark, I am reviving this thread because I am wondering if you ever had any luck getting the 18-bit mode to work with the MCP3421. I can get it working in 16-bit mode but not 18. Any help/update would be appreciated. |
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servera
Joined: 15 Dec 2010
Posts: 2
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| Working MCP3421 code |
| Posted: Wed Dec 15, 2010 8:21 am |
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| Code: | //
// This code setup the MCP3421 in 18bits mode and then enters
// a loop that continually reads and display the value read on
// a 2x20 character LCD.
//
// Use it as a starting point for your own code
//
#include <18F4520.h>
#include <PIC18F4520_registers.h>
#include <stdlib.h>
#include <string.h>
#USE DELAY( clock = 20000000 )
//
// Fuses
//
#FUSES HS // High speed Osc (> 4mhz for PCM/PCH) (>10mhz for PCD)
#FUSES NOFCMEN // Fail-safe clock monitor disabled
#FUSES NOIESO // Internal External Switch Over mode disabled
#FUSES PUT // Power Up Timer
#FUSES NOBROWNOUT // No brownout reset
#FUSES NOWDT // No Watch Dog Timer
#FUSES CCP2B3 // CCP2 input/output multiplexed with RB3
//CCP2C1 CCP2 input/output multiplexed with RC1
#FUSES NOPBADEN // PORTB pins are configured as digital I/O on RESET
//3.09 PBADEN PORTB pins are configured as analog input channels on RESET
#FUSES LPT1OSC // Timer1 configured for low-power operation
#FUSES MCLR // Master Clear pin enabled
#FUSES STVREN // Stack full/underflow will cause reset
//4.00 NOSTVREN Stack full/underflow will not cause reset
#FUSES NOLVP // No low voltage prgming, B3(PIC16) or B5(PIC18) used for I/O
#FUSES NOXINST // Extended set extension and Indexed Addressing mode disabled (Legacy mode)
#FUSES NODEBUG // No Debug mode for ICD
#FUSES NOCPB // No Boot Block code protection
#FUSES NOCPD // No EE protection
#FUSES WRT // Program Memory Write Protected
#FUSES NOWRTC // configuration not registers write protected
#FUSES NOWRTB // Boot block not write protected
#FUSES NOWRTD // Data EEPROM not write protected
#FUSES NOEBTR // Memory not protected from table reads
#FUSES NOEBTRB // Boot block not protected from table reads
#FUSES NOPROTECT // Code not protected from reading
#USE FAST_IO( A )
#USE FAST_IO( B )
#USE FAST_IO( C )
#USE FAST_IO( D )
#USE FAST_IO( E )
#USE RS232( baud = 9600 , xmit = PIN_C6 , rcv = PIN_C7 , bits = 8 , parity = N , ERRORS )
#USE I2C( MASTER , SCL = PIN_C3 , SDA = PIN_C4 )
#ifndef DAL_SCL
#define DAL_SCL PIN_C3
#define DAL_SDA PIN_C4
#endif
void main( void );
void Setup( void );
#define LCD_ENABLE_PIN PIN_A1
#define LCD_RW_PIN PIN_A2
#define LCD_RS_PIN PIN_A3
#define LCD_DATA4 PIN_D4
#define LCD_DATA5 PIN_D5
#define LCD_DATA6 PIN_D6
#define LCD_DATA7 PIN_D7
#include <LCD.c>
//
// 0 means ACK, 1 means NO ACK
//
#define _ACK 0
#define _NOACK 1
void main( void )
{
unsigned char Ack;
char byte0 , byte1 , byte2, conf;
int32 adc_in;
float Volts;
Setup();
lcd_init();
//
// Initialize the MCP3421
//
output_high(DAL_SDA);
output_high(DAL_SCL);
i2c_start();
//
// MCP3421 ADDRESS BYTE - MSB first
//
// 1 - 1 - 0 - 1 - A2 - A1 - A0 - R/W
//
/*
Part Number - Address Option - Code on package
MCP3421A0T-E/CH - A0 (000) - CANN
MCP3421A1T-E/CH - A1 (001) - CBNN
MCP3421A2T-E/CH - A2 (010) - CCNN
MCP3421A3T-E/CH - A3 (011) - CDNN
MCP3421A4T-E/CH - A4 (100) - CENN
MCP3421A5T-E/CH - A5 (101) - CFNN
MCP3421A6T-E/CH - A6 (110) - CGNN
MCP3421A7T-E/CH - A7 (111) - CHNN
*/
//
// Change the address depending on your ADC, check the code on package
// or the invoice from your supplier
//
// 1101XXX0
//
Ack = i2c_write( 0b11010010 ); // Write mode
//
// MCP3421 CONFIGURATION REGISTER - MSB first
// RDY - C1 - C0 - O/C - S1 - S0 - G1 - G0
//
//Ack = i2c_write( 0b00010000 ); // Continuous conversion - 12bit - PGA = 1V/V
Ack = i2c_write( 0b00011100 ); // Continuous conversion - 18bit - PGA = 1V/V
i2c_stop();
//
// Continuous conversion and display on LCD
//
while( 1 )
{
i2c_start();
Ack = i2c_write( 0b11010011 ); // Send address of MCP3421
delay_us( 10 );
//
// NOTE: Don't ack the last byte read
//
byte0 = i2c_read( 1 ); // read first byte and send ack
byte1 = i2c_read( 1 ); // read second byte and send ack
byte2 = i2c_read( 1 ); // read third byte and send ack
conf = i2c_read( 0 ); // read configuration byte - optional
i2c_stop();
//
// Build a int32 from the 3 bytes read
//
byte0 &= 0b00000001; // Mask unused bits, probably not neccesary
adc_in = byte0;
adc_in <<= 8;
adc_in += byte1;
adc_in <<= 8;
adc_in += byte2;
//
// Display the 3 bytes, the conf byte, and adc_in in decimal and hex formats
//
//printf( lcd_putc , "\f%03u, %03u, %03u %X\n%06Lu %LX" , byte0 , byte1 , byte2 , conf , adc_in , adc_in );
//
// Display adc_in in decimal and hex formats
//
printf( lcd_putc , "\f%06Lu %LX" , adc_in , adc_in );
//
// Convert adc_in to Volts
//
/*
Bit Resolutions
12 bits 1 mV
14 bits 250 uV
16 bits 62.5 uV
18 bits 15.625 uV
*/
//Volts = (float)adc_in * 0.001; // 12 bits ADC - NOT TESTED
//Volts = (float)adc_in * 0.000250; // 14 bits ADC - NOT TESTED
//Volts = (float)adc_in * 0.0000625; // 16 bits ADC - NOT TESTED
Volts = (float)adc_in * 0.000015625; // 18 bits ADC
//
// Display the measured voltage
//
printf( lcd_putc , "\nVolts = %04f" , Volts );
delay_ms( 500 );
}
}
void Setup( void )
{
//
// Port configuration. 1 = Inputs, 0 = Outputs. MSB first
//
set_tris_a( 0b11111111 );
set_tris_b( 0b00000001 );
set_tris_c( 0b11111001 );
set_tris_d( 0b00000000 );
set_tris_e( 0b11111111 );
} |
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hasimi20
Joined: 04 Sep 2010
Posts: 19
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| Proteus simulation |
| Posted: Tue Aug 14, 2012 12:12 am |
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I have made a Proteus simulation on servera's program. However the voltage displayed on the lcd just giving a constant value that is "voltage = 2.047984"at any voltage supplied to MCP3421 adc input. My question is
1. Why you include #include <PIC18F4520_registers.h> in the program?what is it contain?
2. If I built the circuit on a breadboard, does it working? |
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Mike Walne
Joined: 19 Feb 2004
Posts: 1785
Location: Boston Spa UK
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| Posted: Tue Aug 14, 2012 2:02 am |
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Why waste time with Proteus?
Use real hardware from the outset.
Mike |
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hasimi20
Joined: 04 Sep 2010
Posts: 19
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| Posted: Tue Aug 14, 2012 2:34 am |
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| thanks for the suggestion |
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