PIC32MX: I2C DAC - Revision history

NickMarchuk: /* Overview */

2010-03-06T18:34:09Z

Overview

NickMarchuk: /* Circuit */

2010-03-06T18:31:53Z

Circuit

NickMarchuk: /* Code */

2010-03-06T18:26:54Z

Code

NickMarchuk at 20:16, 1 March 2010

2010-03-01T20:16:34Z

MatthewLuther: /* Circuit */

2010-02-16T16:44:14Z

Circuit

GabrielHaack: /* Circuit */

2010-02-16T16:39:51Z

Circuit

GabrielHaack: /* Circuit */

2010-02-16T15:42:45Z

Circuit

KrystianZimowski: /* Circuit */

2010-02-16T07:43:24Z

Circuit

KrystianZimowski: /* Circuit */

2010-02-16T07:41:37Z

Circuit

MatthewLuther: /* Overview */

2010-02-16T03:14:22Z

Overview

@@ Line 1: / Line 1: @@
 == Overview ==
-Note: PROJECT NOT FULLY FUNCTIONAL!
 On this page we will present code and a wiring schematic that allows for the PIC32MX to speak to an 8-bit Digital to Analog Converter.  In particular, our project used the MAX518 DAC.
+The MAX518 requires three bytes (note: 1 byte = 8 bits) of information every time it changes its output.  The first byte defines the DAC as a slave, and contains the address.  This byte WILL NOT change when repeatedly sending data to the DAC.  The next byte is the command byte.  The bits are, in order of most significant to least significant: R2, R1, R0, RST, PD, X, X, A0.  R2 = R1 = R0 =0.  This is always true.  The next bit, RST, will reset all registers if set to 1.  Setting PD to 1 will tell the device to hibernate after it outputs the desired data. The next two bits do not matter (X = don't care).  Finally, the address bit, instructing the DAC which output to send the data too. The third byte sent to the MAX518 is the 8 bit value the DAC should output.
-While we were able to send data to the DAC, we were NOT able to elicit output from said DAC.
-This particular DAC, the MAX518 requires three bytes (note: 1 byte = 8 bits) of information every time it changes its output.  The first byte defines the DAC as a slave, and contains the address.  This byte WILL NOT change when repeatedly sending data to the DAC.  The next byte is the actual data the IC should convert.
-The third byte is named the command byte.  The bits are, in order of most significant to least significant: R2, R1, R0, RST, PD, X, X, A0.  R2 = R1 = R0 =0.  This is always true.  The next bit, RST, will reset all registers if set to 1.  Setting PD to 1 will tell the device to hibernate after it outputs the desired data. The next two bits do not matter (X = don't care).  Finally, the address bit, instructing the DAC which output to send the data too.
 == Circuit ==

@@ Line 12: / Line 12: @@
 == Circuit ==
-The circuit was fairly simple after consulting the DAC online data sheets under the practical application wiring diagrams section. The Chip is a MAX 518 Digital to Analog Converter Chip. The two PIC32 NU32 outputs are shown as Serial Data Clock (A14) and Serial Data Output (A15).
+The DAC used is a MAX518 Digital to Analog Converter Chip. The following circuit was used after consulting the MAX518 data sheet under the practical application wiring diagrams section. The two PIC32 NU32 outputs are shown as Serial Data Clock (A14) and Serial Data Output (A15).
-A couple thing to keep in mind; the DAC requires 3.5V to read 'high' at any of its inputs, and the PIC can only put out 3.3V as a theoretical maximum, realistically around 2.7V.  Therefore, a technique known as open drain was used to give the PIC outputs 5V.  The PIC has built-in transistors, so setting the code to open drain will essentially make the output the base current, so that when it goes high, it will saturate the transistor (connected to 5V) sending 5V instead of 3.3V to the emitter, which is connected to the DAC input.  The DAC inputs should be high when not in use, and although the manual says external pull-up resistors are not necessary (we used 10 kohms), one of their example circuits had them, and our circuit only functioned when they were in place.
+One thing to keep in mind: the MAX518 is a 5V chip and requires 3.5V to read 'high' at any of its inputs, and the PIC can only put out 3.3V. Pull up resistors R1 and R2, 1 kOhm, allow the MAX518 to receive data from the PIC. The MAX518 can change its outputs (0 and 1) from 0 to 5V with 8 bit resolution.
 [[Image:I2C Schematic.jpg]]

@@ Line 19: / Line 19: @@
 == Code ==
+This code sets up the I2C to 100kHz and changes output 0 of the MAX518 every 100ms
-Our code is separated into sections, each with sufficient comments to explain all functions
-Our code:
 <pre>
@@ Line 26: / Line 25: @@
 #include <HardwareProfile_NU32.h>
 #include <plib.h>
 // Configuration Bit settings
@@ Line 35: / Line 33: @@
 // Other options are don't care
 //
-#pragma config FPLLMUL = MUL_20, FPLLIDIV = DIV_2, FPLLODIV = DIV_1, FWDTEN = OFF
+//#pragma config FPLLMUL = MUL_20, FPLLIDIV = DIV_2, FPLLODIV = DIV_1, FWDTEN = OFF
-#pragma config POSCMOD = HS, FNOSC = PRIPLL, FPBDIV = DIV_2
+//#pragma config POSCMOD = HS, FNOSC = PRIPLL, FPBDIV = DIV_2
+//#define SYSCLK (80000000) // set system clock to 80MHz
-// DEFINES
+//#define PBCLK (SYSCLK/1000) // set PBCLK to 80 KHz
+#define FPB SYS_FREQ // Result of bootloader
-#define SYSCLK	(80000000) // set system clock to 80MHz
+#define I2CBAUD 100000 // 100 kHz clock
+#define BRG_VAL ((SYS_FREQ/2/I2CBAUD)-2)
-#define PBCLK  (SYSCLK/1000) // set PBCLK to 80 KHz
+void Delayms( unsigned t)
-#define Fsck	50000
+// This uses Timer 1, can be changed to another timer. Assumes FPB = SYS_FREQ
-#define BRG_VAL 	((PBCLK/2/Fsck)-2)
+{
+    OpenTimer1(T1_ON | T1_PS_1_256, 0xFFFF);
-#define Nop() asm( "nop" )  //allows for a pause command
+    while (t--)
+    {  // t x 1ms loop
-// a simple puase command
+        WriteTimer1(0);
-void i2c_wait(unsigned int cnt)
+        while (ReadTimer1() < FPB/256/1000);
-{
+	}
-	while(--cnt)
+	CloseTimer1();
-	{
+} // Delayms
-		Nop();
-		Nop();
-	}
-}
-/////////////////////////////////////////////
-/////////////////////////////////////////////
 int main(void)
-{
-	ODCA = 0xC000;
-	unsigned char SlaveAddress;
-	char i2cData[3];
-	//Enable channel using default values
-	OpenI2C1( I2C_EN, BRG_VAL );
-	SlaveAddress = 0x58;
-	i2cData[0] = ((SlaveAddress ));
-	i2cData[1] = 0x05; //command line
-	i2cData[2] = 0xFF; //end command
-while(1) // run the code over and over again
 {
+    ODCA = 0xC000;
+    unsigned char addr = 0x58;
+    //Enable channel using default values
+    OpenI2C1( I2C_EN, BRG_VAL );
+    unsigned char cmd = 0; //command line
+    unsigned char data = 0; //output data, digital value to be converted
+    SYSTEMConfigPerformance(SYS_FREQ); // tell PIC its operating frequency
+    mInitAllLEDs(); // initialize LEDs on NU32 board, defined in HardwareProfile_NU32.h
+    mInitAllSwitches(); // initialize switches on NU32 board
+    while(1) // run the code over and over again
+    {
-	StartI2C1();	//Send the Start Bit (begin of data send)
+        // start the I2C communication
-	IdleI2C1();		//Wait to complete
+        StartI2C1(); // Send the Start Bit (begin of data send)
-	MasterWriteI2C1 (i2cData[0]); //address
-	IdleI2C1();
+        IdleI2C1(); // Wait to complete
-	AckI2C1(); //ask for acknowledge bit before continuing
+        // write the address of the chip, defined by pins AD0 and AD1 on the MAX518
-	MasterWriteI2C1 (i2cData[1]); //command line
+        MasterWriteI2C1 (addr); // address
-	IdleI2C1();
+        IdleI2C1();
-	AckI2C1();
+        while( !I2C1STATbits.ACKSTAT==0 ){}
-	MasterWriteI2C1(i2cData[2]); //output
-	IdleI2C1();
+        // write the command to tell the MAX518 to change its output on output 0
-	AckI2C1();
+        MasterWriteI2C1 (cmd); // command line
-	StopI2C1();  //end of data send
+        IdleI2C1();
+        while( !I2C1STATbits.ACKSTAT==0 ){}
-}
-}
+        // wite the value to put on the output
+        MasterWriteI2C1(data); // output
+        IdleI2C1();
+        while( !I2C1STATbits.ACKSTAT==0 ){}
+        // end the I2C communication
+        StopI2C1(); // end of data send
+        IdleI2C1(); // Wait to complete
+        // the total write time is ~285us with an I2C clock of 100 kHz
+        data++; // increase the data, make a sawtooth wave as an example
+        Delayms(100);
+        //if(data>255) { // don't have to worry about this, data is 8 bit so it will roll over automatically
+        //    data=0;
+        //}
+    } // end while(1)
+} // end main
 </pre>

@@ Line 1: / Line 1: @@
-== Original Assignment ==
-'''Do not erase this section!'''
-Your assignment is to interface to the MAX518 I2C digital to analog converter (DAC).
 == Overview ==
 Note: PROJECT NOT FULLY FUNCTIONAL!

@@ Line 20: / Line 20: @@
 The circuit was fairly simple after consulting the DAC online data sheets under the practical application wiring diagrams section. The Chip is a MAX 518 Digital to Analog Converter Chip. The two PIC32 NU32 outputs are shown as Serial Data Clock (A14) and Serial Data Output (A15).
-A couple thing to keep in mind; the DAC requires 3.5V to read 'high' at any of its inputs, and the PIC can only put out 3.3V as a theoretical maximum, realistically around 2.7V.  Therefore, a technique known as open drain was used to give the PIC outputs 5V.  The PIC has built-in transistors, so setting the code to open drain will essentially make the output the base current, so that when it goes high, it will saturate the transistor (connected to 5V) sending 5V instead of 3.3V to the emitter, which is connected to the DAC input.  The DAC inputs should be high when not in use, and although the manual says external pull-up resistors are not necessary, one of their example circuits had them, and our circuit only functioned when they were in place.
+A couple thing to keep in mind; the DAC requires 3.5V to read 'high' at any of its inputs, and the PIC can only put out 3.3V as a theoretical maximum, realistically around 2.7V.  Therefore, a technique known as open drain was used to give the PIC outputs 5V.  The PIC has built-in transistors, so setting the code to open drain will essentially make the output the base current, so that when it goes high, it will saturate the transistor (connected to 5V) sending 5V instead of 3.3V to the emitter, which is connected to the DAC input.  The DAC inputs should be high when not in use, and although the manual says external pull-up resistors are not necessary (we used 10 kohms), one of their example circuits had them, and our circuit only functioned when they were in place.
 [[Image:I2C Schematic.jpg]]