Overview
The Dallas DS1803 is a dual potentiometer which is controlled using the Philips I2C protocol.
More details on the operation in the context of a Parallax BASIC Stamp 2 appears elsewhere on this web site.
// DS1803_1.BS2
//
// Illustrates how to control DS1803 Addressable Dual Potentiometer
//
// 16F84 DS1803
//
// RB.1 (term 7) ------------------- SCL (term 9) ----- To Other
// RB.0 (term 6) ------------------- SDA (term 10) ----- I2C Devices
//
// Note that the slave address is determined by A2 (term 4), A1 (term 5)
// and A0 (term 6) on the 1803. The above SCL and SDA leads may be multipled
// to eight devices, each strapped for a unique A2 A1 A0 setting. In this
// program A2, A1 and A0 are connected to ground.
//
// Pot 0 is set to a value of $55 and Pot 1 to $80. The settings of the
// two pots are then read from the 1803 and displayed on a serial LCD on
// RA.0.
//
// Note that in function ds1803_read_pots the settings are returned to
// calling function using pointers.
//
// copyright Peter H. Anderson, Baltimore, MD, April, '99
#case
#include <16f84.h>
#include <string.h>
#include <defs_f84.h>
void ds1803_write_pot(int device, int pot, int setting);
void ds1803_read_pots(int device, int *p_setting_0, int *p_setting_1);
// common i2c routines
byte i2c_in_byte(void);
void i2c_out_byte(byte o_byte);
void i2c_nack(void);
void i2c_ack(void);
void i2c_start(void);
void i2c_stop(void);
void i2c_high_sda(void);
void i2c_low_sda(void);
void i2c_high_scl(void);
void i2c_low_scl(void);
// delay routines
void delay_ms(long t);
void delay_10us(int t);
// LCD routines
void lcd_init(void);
void out_RAM_str(int *s);
void lcd_hex_byte(int val);
void lcd_dec_byte(int val, int digits);
int num_to_char(int val);
void lcd_char(int ch);
void lcd_new_line(void);
#define TxData 0 // RA.0 for serial LCD
#define SDA_PIN rb0 // RB.0
#define SCL_PIN rb1 // RB.1
#define SDA_DIR trisb0
#define SCL_DIR trisb1
void main(void)
{
int pot_setting_0, pot_setting_1;
ds1803_write_pot(0, 0, 0x55); // dev 0, pot 0, setting 0x55
ds1803_write_pot(0, 1, 0x80);
ds1803_read_pots(0, &pot_setting_0, &pot_setting_1);
lcd_init();
lcd_hex_byte(pot_setting_0);
lcd_char(' ');
lcd_hex_byte(pot_setting_1);
delay_ms(500);
}
void ds1803_write_pot(int device, int pot, int setting)
//writes specified setting to specified potentiometer on specified device
{
i2c_start();
i2c_out_byte(0x50 | (device << 1));
i2c_nack();
i2c_out_byte(0xa9 + pot); // 0xa9 for pot 0, 0xaa for pot 1
i2c_nack();
i2c_out_byte(setting);
i2c_nack();
i2c_stop();
delay_ms(25);
}
void ds1803_read_pots(int device, int *p_setting_0, int *p_setting_1)
//reads data from both potentiometers
{
i2c_start();
i2c_out_byte(0x51 | (device << 1));
i2c_nack();
*p_setting_0 = i2c_in_byte();
i2c_ack();
*p_setting_1 = i2c_in_byte();
i2c_ack();
i2c_stop();
}
// Common I2C Routines
byte i2c_in_byte(void)
{
byte i_byte, n;
i2c_high_sda();
for (n=0; n<8; n++)
{
i2c_high_scl();
if (SDA_PIN)
{
i_byte = (i_byte << 1) | 0x01; // msbit first
}
else
{
i_byte = i_byte << 1;
}
i2c_low_scl();
}
return(i_byte);
}
void i2c_out_byte(byte o_byte)
{
byte n;
for(n=0; n<8; n++)
{
if(o_byte&0x80)
{
i2c_high_sda();
}
else
{
i2c_low_sda();
}
i2c_high_scl();
i2c_low_scl();
o_byte = o_byte << 1;
}
i2c_high_sda();
}
void i2c_nack(void)
{
i2c_high_sda(); // data at one
i2c_high_scl(); // clock pulse
i2c_low_scl();
}
void i2c_ack(void)
{
i2c_low_sda(); // bring data low and clock
i2c_high_scl();
i2c_low_scl();
i2c_high_sda();
}
void i2c_start(void)
{
i2c_low_scl();
i2c_high_sda();
i2c_high_scl(); // bring SDA low while SCL is high
i2c_low_sda();
i2c_low_scl();
}
void i2c_stop(void)
{
i2c_low_scl();
i2c_low_sda();
i2c_high_scl();
i2c_high_sda(); // bring SDA high while SCL is high
// idle is SDA high and SCL high
}
void i2c_high_sda(void)
{
// bring SDA to high impedance
SDA_DIR = 1;
delay_10us(5);
}
void i2c_low_sda(void)
{
SDA_PIN = 0;
SDA_DIR = 0; // output a hard logic zero
delay_10us(5);
}
void i2c_high_scl(void)
{
SCL_DIR = 1; // high impedance
delay_10us(5);
}
void i2c_low_scl(void)
{
SCL_PIN = 0;
SCL_DIR = 0;
delay_10us(5);
}
// delay routines
void delay_10us(int t)
{
#asm
BCF STATUS, RP0
DELAY_10US_1:
CLRWDT
NOP
NOP
NOP
NOP
NOP
NOP
DECFSZ t, F
GOTO DELAY_10US_1
#endasm
}
void delay_ms(long t) // delays t millisecs
{
do
{
delay_10us(100);
} while(--t);
}
// LCD routines
int num_to_char(int val) // converts val to hex character
{
int ch;
if (val < 10)
{
ch=val+'0';
}
else
{
val=val-10;
ch=val + 'A';
}
return(ch);
}
void lcd_char(int ch) // serial output to PIC-n-LCD, 9600 baud
{
int n, dly;
// start bit + 8 data bits
#asm
BCF STATUS, RP0
MOVLW 9
MOVWF n
BCF STATUS, C
LCD_CHAR_1:
BTFSS STATUS, C
BSF PORTA, TxData
BTFSC STATUS, C
BCF PORTA, TxData
MOVLW 32
MOVWF dly
LCD_CHAR_2:
DECFSZ dly, F
GOTO LCD_CHAR_2
RRF ch, F
DECFSZ n, F
GOTO LCD_CHAR_1
BCF PORTA, TxData
CLRWDT
MOVLW 96
MOVWF dly
LCD_CHAR_3:
DECFSZ dly, F
GOTO LCD_CHAR_3
CLRWDT
#endasm
}
// LCD routines
void lcd_init(void) // sets TxData in idle state and resets PIC-n-LCD
{
#asm
BCF STATUS, RP0
BCF PORTA, TxData
BSF STATUS, RP0
BCF TRISA, TxData
BCF STATUS, RP0
#endasm
lcd_char(0x0c);
delay_ms(250);
}
void lcd_new_line(void) // outputs 0x0d, 0x0a
{
lcd_char(0x0d);
delay_ms(10); // give the PIC-n-LCD time to perform the
lcd_char(0x0a); // new line function
delay_ms(10);
}
void out_RAM_str(int *s)
{
while(*s)
{
lcd_char(*s);
++s;
}
}
void lcd_hex_byte(int val) // displays val in hex format
{
int ch;
ch = num_to_char((val>>4) & 0x0f);
lcd_char(ch);
ch = num_to_char(val&0x0f);
lcd_char(ch);
}
void lcd_dec_byte(int val, int digits)
// displays byte in decimal as either 1, 2 or 3 digits
{
int d;
int ch;
if (digits == 3)
{
d=val/100;
ch=num_to_char(d);
lcd_char(ch);
}
if (digits >1) // take the two lowest digits
{
val=val%100;
d=val/10;
ch=num_to_char(d);
lcd_char(ch);
}
if (digits == 1) // take the least significant digit
{
val = val%100;
}
d=val % 10;
ch=num_to_char(d);
lcd_char(ch);
}