Diff: MCP4822.cpp

Revision:

0:a10e8793cf0a

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MCP4822.cpp	Thu Jun 14 03:58:16 2012 +0000
@@ -0,0 +1,61 @@
+#include "MCP4822.h"
+
+//initialization function
+MCP4822::MCP4822(int SPIchannelNum, PinName _CS, PinName _LDAC) : DAC_SPI(SPIchannelNum, _CS, _LDAC){    
+    messageBits(16);
+    frequency(20000000);    
+    autoUpdate=1;
+    gain =0; //set gain to x2 to get full range
+}
+
+void MCP4822::select(char DACnum){
+    DACselect=DACnum & 0x01; //choose between DAC A and DAC B
+}
+
+void MCP4822::write_mv(int mVolts){  //since out reference diode is at 4.096V, we can directly map our voltage values to DAC values when gain is set to x2.
+    if (gain==0){ //gain is x2
+        write(mVolts);
+    }
+    else{ //gain is x1
+        write(mVolts*2);
+    }
+}
+
+void MCP4822::write(int value){
+    //valid voltage values are up to 4096mV.  We directly map our value to mV.  
+    //All serial commands are 16 bit words.   The highest 4 bits are control bits, while the last 12 are the data bits for the 12-bit DAC MCP4822.
+    //bit 15: select which DAC to use.
+    //bit 14: unused
+    //bit 13: 0= gain x2, 1= gain x1
+    //bit 12: 0= DAC active, 1= shut down DAC
+    //bit 11-0: Data bits for the DAC.
+    if (value > 0xFFF){
+        value = 0xFFF;  //any out of range values will be truncated to our max value
+    }      
+    
+    value=value & 0xFFF; //limit our value to 12 bits.
+    //SCK=0;  //set the clock low.   Data is read on the rising edge of the clock.
+    LDAC=1;
+    CS=0; //enable the chip to recieve data
+    char controlbits=(DACselect<<3)+(gain<<1) +1;
+    
+    int message= (controlbits<<12)+value;
+    (*DACspi).write(message);
+    CS=1;  //signal end of message.   The data will be loaded into the internal registers.
+    if(autoUpdate){ LDAC=0;} //trigger the update of the output voltage.
+      
+}
+void MCP4822::update(){
+    //triggers the DAC to update output on command.   Useful if we wish to synchronize the DAC output value with another event.
+    LDAC=0;
+}
+
+//Set the multiplying factor for the output.  Valid inputs are gains of 1 and 2.*/
+void MCP4822::setGain(int gain_value){
+    if (gain_value>1){ 
+        gain =1; //Set gain to x2
+    }
+    else{
+        gain=0; //Set gain to x1.   Limits range to 2.098mV
+    }
+}
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