Revision 0:b74d88185698, committed 2012-07-03

Comitter:

JimmyTheHack

Date:

Tue Jul 03 03:22:59 2012 +0000

Child:

1:90b59ae53d25

Commit message:

updated DAC_SPI library to have virtual select function

Changed in this revision

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/DAC_SPI/DAC_SPI.cpp	Tue Jul 03 03:22:59 2012 +0000
@@ -0,0 +1,39 @@
+#ifndef DAC_SPI_CPP
+#define DAC_SPI_CPP
+
+#include "DAC_SPI.h"
+/*SPI Channels */
+                          //since we only have two SPI channels, which must be shared, define them here.  
+SPI SPI_A(p5, NC, p7);    //If using with other serial devices, can pass a pointer to the serial channel.
+SPI SPI_B(p11, NC, p13);
+
+/*Initialize DAC */
+DAC_SPI::DAC_SPI(int SPIchannelNum, PinName _CS, PinName _LDAC) : CS(_CS), LDAC(_LDAC){  
+    if (SPIchannelNum ==1){
+        DACspi = &SPI_B;
+    }  
+    else{
+        DACspi = &SPI_A;
+    }
+    messageBits(16);
+}
+
+/** Manually change the SPI frequency 
+* Must be a value supported by the mbed and DAC
+*/
+void DAC_SPI::frequency(int freq){
+    (*DACspi).frequency(freq);    
+}
+
+
+//specify the number of bits used in message packets to the DAC.
+void DAC_SPI::messageBits(int bits){
+    (*DACspi).format(bits,0);
+}
+
+//select a DACnum for use with chips with multiple onboard DACs.
+void DAC_SPI::select(char DACnum){
+    DACselect=DACnum;
+}
+
+#endif //DAC_SPI_CPP
\ No newline at end of file

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/DAC_SPI/DAC_SPI.h	Tue Jul 03 03:22:59 2012 +0000
@@ -0,0 +1,33 @@
+#ifndef DAC_SPI_H
+#define DAC_SPI_H
+#include "mbed.h"
+
+/* a basic parent library for use with DACs controlled via SPI.  Individual hardware implementations will need their own libraries.
+This provides basic initialization of common pins and provides a serial channel.   Doesn't provide a lot of added functionality, but serves as an interface for the SPI library.
+*/
+class DAC_SPI
+{
+    public:
+    DAC_SPI(int SPIchannelNum, PinName CS,  PinName LDAC);
+    virtual void select(char DACvalue); //choose the active DAC
+    virtual void write(int DACvalue) =0; //write a value to the Digital Analog Converter    
+    virtual void write_mV(int millivolts) =0; //write a value to the Digital Analog Converter specified in mV (may require appropriate scaling factor)
+    
+    /** Manually change the SPI frequency 
+    * @param freq Desired frequency in hertz: must be a value supported by both the mbed and DAC.  The MCP4922 supports frequencies to 20MHz.
+    */
+    void frequency(int freq);
+    //set the number of bits for DAC
+    void messageBits(int bits);
+    //DigitalOut SCK;
+    /** The currently selected DAC channel.  0 for DAC A, 1 for DAC B, etc*/
+    char DACselect;
+    DigitalOut CS;  //serial chip select pin
+    DigitalOut LDAC; //synchronize pin to update both DACs together    
+    SPI * DACspi;  //SPI channel.  0 for p5-p7, 1 for p11-p13
+};
+
+extern SPI SPI_A;  //channel A SPI (pins 5,7)
+extern SPI SPI_B;  //channel B SPI (pins 11,13)
+
+#endif //DAC_H
\ No newline at end of file

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MAX500.cpp	Tue Jul 03 03:22:59 2012 +0000
@@ -0,0 +1,61 @@
+#include "MAX500.h"
+
+MAX500::MAX500(int SPIchannelNum, PinName _LOAD, PinName _LDAC) : DAC_SPI(SPIchannelNum, _LOAD, _LDAC){   //We use the 3 wire serial interface, since the timing is more standardized. 
+    (*DACspi).format(10,2);  //messages use a 10 bit word, and read data on the falling edge with the clock defaulting to HIGH.
+    frequency(5000000);  //set default frequency to 5MHz since unstated   
+    autoUpdate=1;
+    VrefAB=5000; //assume a 5V reference voltage for use with write_mv().  This value can be configured;
+    VrefC=5000; //assume a 5V reference voltage for use with write_mv().  This value can be configured;
+    VrefD=5000; //assume a 5V reference voltage for use with write_mv().  This value can be configured;
+    CS=1; //CS is our LOAD pin
+}
+
+void MAX500::select(char DACnum){
+    DACselect=DACnum & 0x03; //choose between DAC A , B, C or D
+}
+
+void MAX500::write_mV(int mV){
+    int Vref;
+    if (DACselect==0 || DACselect ==1){
+        Vref=VrefAB;
+    }
+    else if (DACselect ==2) {
+        Vref=VrefC;
+    }
+    else{
+        Vref=VrefD;
+    }
+    int DACvalue= mV* 255/Vref ; //scale voltage to a DAC value.
+    write(DACvalue);
+}
+
+void MAX500::write(int value){
+    //valid input values are 0 - 255.   255 should scale to Vref.   
+    //All serial commands are 10 bit words.   The highest 2 bits are control bits, while the last 8 are the data bits for the 8-bit DAC MAX500.
+
+    //bit 9-8: Selection bits for DAC
+    //bit 7-0: Data bits for the DAC.
+    
+    if (value > 0x0FF){
+        value = 0x0FF;  //any out of range values will be truncated to our max value
+    }    
+    value=value & 0x0FF; //limit our value to 8 bits.
+    
+    //SCK=0;  //set the clock low.    
+    LDAC=1;
+    CS=1; //enable the chip to recieve data    
+    
+    int message= (DACselect<<8)+value;
+    (*DACspi).write(message);
+    //wait_us(5);
+    CS=0;  //signal end of message.   The data will be loaded into the internal registers.
+    //wait_us(5);
+    CS=1;
+    if(autoUpdate){ LDAC=0;} //trigger the update of the output voltage.
+      
+}
+void MAX500::update(){
+    //triggers the DAC to update output on command.   Useful if we wish to synchronize the DAC output value with another event.
+    LDAC=0;
+}
+

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MAX500.h	Tue Jul 03 03:22:59 2012 +0000
@@ -0,0 +1,78 @@
+#ifndef MAX500_H
+#define MAX500_H
+
+#include "DAC_SPI.h"
+
+/** 
+* The MAX500 is a quad package 8 bit DAC.  We should be able to produce four analog output voltages up to the externally wired voltage references (VrefA/B, VrefC, VrefD).
+ The maximum voltage output is recommended to be about 4V less than the power supply voltage, although getting a 12V output from a 15V power supply is possible.  
+*
+* Datasheet: http://datasheets.maxim-ic.com/en/ds/MAX500.pdf
+*
+* We use the "3-wire" serial interface since it seems to be more compatible with the mbed Serial library timing than the "2-wire" interface.  The 2-wire interface uses a somewhat non-standard timing scheme
+* and may require custom code support.
+*
+* All serial commands are 10 bit words.   The highest 2 bits are control bits, while the last 8 are the data bits for the 8-bit DAC MAX500.   
+*    + bit 13-12: choose which DAC to use
+*    + bit 11-0: Data bits for the DAC.
+*/
+class MAX500: public DAC_SPI
+{    
+    public:
+    
+    /** Initializes the MAX 500 DAC 
+    *
+    * @param SPIchannelNum An int representing the SPI channel used by this DAC
+    * channel 0 for p5 and p7
+    * channel 1 for p11 and p13
+    * @param LOAD The chip select pin (CS) used to identify the device
+    * @param LDAC The LDAC pin used to synchronize updates of multiple devices
+    */
+    MAX500(int SPIchannelNum, PinName LOAD,  PinName LDAC);
+    
+    /** Writes a value between 0-255 to the currently selected DAC output 
+    * @param DACvalue a value from 0-255 to write to the DAC register
+    */
+    virtual void write(int DACvalue);
+    
+    /** Writes a value in mV to the DAC outputs.
+    * The output will only be accurate if Vref is set to the appropriate voltage reference scaling factor. 
+    * @param millivolts The desired voltage output in millivolts
+    */
+    virtual void write_mV(int millivolts); 
+    
+    /** If automatic updating is disabled, this will update the DAC output on command */
+    void update();    
+    
+    /** select whether to use DAC A or DAC B. 
+    * @param DACnum 0 to modify DAC A, 1 to modify DAC B
+    */
+    virtual void select(char DACnum); 
+    
+    /** If true, the DAC output will update as soon as the output value is modified.  If false, it will wait for an update command*/
+    bool autoUpdate;
+    
+    /** The currently selected DAC channel.  0 for DAC A, 1 for DAC B*/
+    char DACselect;
+    
+    /** The output scaling factor in mV for channels A and B.
+    * The voltage wired to Vref will be used as the scaling factor which the DAC will use in producing the output voltage.
+    * If using the write_mV function, it is important that Vref is properly set.  This library uses 5000mV by default.
+    */
+    int VrefAB;
+    /** The output scaling factor in mV for channel C.
+    * The voltage wired to Vref will be used as the scaling factor which the DAC will use in producing the output voltage.
+    * If using the write_mV function, it is important that Vref is properly set.  This library uses 5000mV by default.
+    */
+    int VrefC;
+    /** The output scaling factor in mV for channel D.
+    * The voltage wired to Vref will be used as the scaling factor which the DAC will use in producing the output voltage.
+    * If using the write_mV function, it is important that Vref is properly set.  This library uses 5000mV by default.
+    */    
+    int VrefD;
+    
+    
+    
+};
+
+#endif //MAX500_H
\ No newline at end of file