MCP4922.h

00001 #ifndef MCP4922_H
00002 #define MCP4922_H
00003 
00004 #include "DAC_SPI.h"
00005 
00006 /** 
00007 * The MCP4922 is a dual package 12 bit DAC.  We should be able to produce two analog output voltages up to twice the externally wired voltage references (VrefA, VrefB).
00008  The maximum voltage output is limited by the input voltage at V_DD which can go up to about 5.5V.  
00009 
00010 * Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/22250A.pdf
00011 
00012 * 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.
00013 *    + bit 15: select which DAC to use.
00014 *    + bit 14: 0=buffered , 1= unbuffered
00015 *    + bit 13: 0= gain x2, 1= gain x1
00016 *    + bit 12: 0= DAC active, 1= shut down DAC
00017 *    + bit 11-0: Data bits for the DAC.
00018 */
00019 class MCP4922: public DAC_SPI
00020 {    
00021     public:
00022     
00023     /** Initializes the MCP 4922 DAC 
00024     *
00025     * @param SPIchannelNum An int representing the SPI channel used by this DAC
00026     * channel 0 for p5 and p7
00027     * channel 1 for p11 and p13
00028     * @param CS The chip select pin used to identify the device
00029     * @param LDAC The LDAC pin used to synchronize updates of multiple devices
00030     */
00031     MCP4922(int SPIchannelNum, PinName CS,  PinName LDAC);
00032     
00033     /** Writes a value between 0-4095 to the currently selected DAC output 
00034     * @param DACvalue a value from 0-4095 to write to the DAC register
00035     */
00036     virtual void write(int DACvalue);
00037     
00038     /** Writes a value in mV to the DAC outputs.
00039     * The output will only be accurate if Vref is set to the appropriate voltage reference scaling factor. 
00040     * @param millivolte The desired voltage output in millivolts
00041     */
00042     virtual void write_mV(int millivolts); 
00043     
00044     /** If automatic updating is disabled, this will update the DAC output on command */
00045     void update();    
00046     
00047     /** select whether to use DAC A or DAC B. 
00048     * @param DACnum 0 to modify DAC A, 1 to modify DAC B
00049     */
00050     virtual void select(char DACnum); 
00051     
00052     /** If true, the DAC output will update as soon as the output value is modified.  If false, it will wait for an update command*/
00053     bool autoUpdate;
00054     
00055     /** The currently selected DAC channel.  0 for DAC A, 1 for DAC B*/
00056     char DACselect;
00057     
00058     /** The output scaling factor in mV for channel A.
00059     * The voltage wired to Vref will be used as the scaling factor which the DAC will use in producing the output voltage.
00060     * If using the write_mV function, it is important that Vref is properly set.  This library uses 5000mV by default.
00061     */
00062     int VrefA;
00063     /** The output scaling factor in mV for channel B.
00064     * The voltage wired to Vref will be used as the scaling factor which the DAC will use in producing the output voltage.
00065     * If using the write_mV function, it is important that Vref is properly set.  This library uses 5000mV by default.
00066     */
00067     int VrefB;
00068     
00069     /** Manually set the gain of the DAC.  The only valid values are 1 and 2.   The default gain is x1 to match the wired reference voltage*/
00070     void setGain(int gain_value);
00071     
00072     /** Turn on or off the output buffer.  The default value for the buffer is off.  See section 4.1.2 of the datasheet for more information. */
00073     char buffered;
00074     
00075     private:
00076     /** The output gain bit of the DAC.  If set to 0, gain is x2. If set to 1 gain is x1.  The default gain is 1.*/
00077     bool gain;
00078 };
00079 
00080 #endif //MCP4922_H