MCP4822A.cpp

00001 /*
00002  * MCP4822A - DAC array library.
00003  *
00004  * Copyright (c) 2011 Steven Beard, UK Astronomy Technology Centre.
00005  *
00006  * Permission is hereby granted, free of charge, to any person obtaining a copy
00007  * of this software and associated documentation files (the "Software"), to deal
00008  * in the Software without restriction, including without limitation the rights
00009  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
00010  * copies of the Software, and to permit persons to whom the Software is
00011  * furnished to do so, subject to the following conditions:
00012  *
00013  * The above copyright notice and this permission notice shall be included in
00014  * all copies or substantial portions of the Software.
00015  *
00016  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
00017  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
00018  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
00019  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
00020  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
00021  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
00022  * THE SOFTWARE.
00023  */
00024 
00025 #include "mbed.h"
00026 #include "MCP4822A.h"
00027 
00028 using namespace mbed;
00029 
00030 /*+
00031  * Interface to an array of MCP4822 12-bit dual-output DACs daisy chained
00032  * on an SPI bus and selected using DigitalOut pins.
00033  *
00034  * For a detailed API description see MCP4822.h.
00035  *-
00036  */
00037 // Constructor
00038 MCP4822A::MCP4822A(int ndacs, PinName mosi, PinName sclk, PinName ncslist[], PinName nldac) : _spi(mosi, NC, sclk) {
00039 
00040     // Create an array of DigitalOut objects connected to each NCS pin.
00041     int i;
00042     _ndacs = (ndacs > 0) ? ndacs : 1;
00043     _ncs_array = new DigitalOut*[ _ndacs ];
00044     for (i=0; i<_ndacs; i++) {
00045         _ncs_array[i] = new DigitalOut( ncslist[i] );
00046     }
00047 
00048     // The LDAC pin is optional.
00049     if (nldac == NC) {
00050         // LDAC is not connected for this DAC.
00051         _latched = 0;
00052         _nldac = NULL;
00053     } else {
00054         // LDAC is connected - create a DigitalOut object connected to it.
00055         _latched = 1;
00056         _nldac = new DigitalOut( nldac );
00057     }
00058 
00059     // Initialise the DAC SPI interface.
00060     _init();
00061 }
00062 
00063 // Destructor
00064 MCP4822A::~MCP4822A() {
00065 
00066     // Before destroying the object, shut down all the chips.
00067     shdn_all();
00068 
00069     // Delete all the NCS DigitalOut objects and the array pointing to
00070     // them.
00071     int i;
00072     for (i=0; i<_ndacs; i++) {
00073         delete _ncs_array[i];
00074     }
00075     delete [] _ncs_array;
00076 
00077     // Delete the LDAC DigitalOut object if it exists.
00078     if (_latched ) delete _nldac;
00079 }
00080 
00081 // Initialise SPI interface.
00082 void MCP4822A::_init() {
00083 
00084     // Set up the SPI for 16-bit values (12-bit + 4 command bits) and mode 0.
00085     _spi.format(16, 0);
00086 
00087     // Start with all the CS and LDAC signals high (disabled)
00088     int i;
00089     for (i=0; i<_ndacs; i++) {
00090         _ncs_array[i]->write(1);
00091     }
00092 
00093     if (_latched ) _nldac->write(1);
00094     return;
00095 }
00096 
00097 // Set SPI clock frequency.
00098 void MCP4822A::frequency( int freq ) {
00099 
00100     // Set the SPI interface clock frequency in Hz.
00101     _spi.frequency( freq );
00102     return;
00103 }
00104 
00105 /*
00106  * Note: There is a lot of code in common between the following 4 functions.
00107  * The code is kept in line to keep it efficient. Could the functions have
00108  * been written as templates?
00109  */
00110 // Write to DAC channel A with gain 1.
00111 void MCP4822A::writeA1(int dac, int value) {
00112 
00113     // Set up the command register with the appropriate value.
00114     // For efficiency, the caller is assumed to have checked dac.
00115     int reg;
00116     reg = (value & 0x0FFF) | MCP4822_REG_A1;
00117 
00118     // Select the DAC chip, write to its command register and
00119     // then unselect the DAC chip.
00120     _ncs_array[dac]->write(0);
00121     _spi.write(reg);
00122     _ncs_array[dac]->write(1);
00123     return;
00124 }
00125 
00126 // Write to DAC channel A with gain 2.
00127 void MCP4822A::writeA2(int dac, int value) {
00128 
00129     // Set up the command register with the appropriate value.
00130     // For efficiency, the caller is assumed to have checked dac.
00131     int reg;
00132     reg = (value & 0x0FFF) | MCP4822_REG_A2;
00133 
00134     // Select the DAC chip, write to its command register and then
00135     // unselect the DAC chip.
00136     _ncs_array[dac]->write(0);
00137     _spi.write(reg);
00138     _ncs_array[dac]->write(1);
00139     return;
00140 }
00141 
00142 // Write to DAC channel B with gain 1.
00143 void MCP4822A::writeB1(int dac, int value) {
00144 
00145     // Set up the command register with the appropriate value.
00146     // For efficiency, the caller is assumed to have checked dac.
00147     int reg;
00148     reg = (value & 0x0FFF) | MCP4822_REG_B1;
00149 
00150     // Select the DAC chip, write to its command register and then
00151     // unselect the DAC chip.
00152     _ncs_array[dac]->write(0);
00153     _spi.write(reg);
00154     _ncs_array[dac]->write(1);
00155     return;
00156 }
00157 
00158 // Write to DAC channel B with gain 2.
00159 void MCP4822A::writeB2(int dac, int value) {
00160 
00161     // Set up the command register with the appropriate value.
00162     // For efficiency, the caller is assumed to have checked dac.
00163     int reg;
00164     reg = (value & 0x0FFF) | MCP4822_REG_B2;
00165 
00166     // Select the DAC chip, write to its command register and then
00167     // unselect the DAC chip.
00168     _ncs_array[dac]->write(0);
00169     _spi.write(reg);
00170     _ncs_array[dac]->write(1);
00171     return;
00172 }
00173 
00174 // Write an array of values to the DACs.
00175 void MCP4822A::write(int nchans, int values[], int gain, int latch) {
00176 
00177     // nchans must be at least 1 but less than or equal to ndacs x 2.
00178     if (nchans < 1) nchans = 1;
00179     const int maxchans = _ndacs * 2;
00180     if (nchans > maxchans) nchans = maxchans;
00181 
00182     if (latch && _latched)
00183         latch_disable();
00184 
00185     int i, dac;
00186     if ( gain == 2 ) {
00187 
00188         for (i=0; i<nchans;) {
00189             dac = i/2;
00190             writeA2(dac, values[i]);
00191             i++;
00192             if (i < nchans) {
00193                 writeB2(dac, values[i]);
00194                 i++;
00195             } else break;
00196         }
00197     } else {
00198 
00199         for (i=0; i<nchans;) {
00200             dac = i/2;
00201             writeA1(dac, values[i]);
00202             i++;
00203             if (i < nchans) {
00204                 writeB1(dac, values[i]);
00205                 i++;
00206             } else break;
00207         }
00208     }
00209 
00210     // Automatically latch the new voltages if the latch flag is 1.
00211     if (latch && _latched)
00212         latch_enable();
00213     return;
00214 }
00215 
00216 // Convert a voltage into a 12-bit value.
00217 int MCP4822A::voltage2value( float voltage, int gain ) {
00218 
00219     int value = int(4096000.0 * abs(voltage) / float(MCP4822_VREF * gain));
00220     if ( value > 0x0FFF ) value = 0x0FFF;
00221     return value;
00222 }
00223 
00224 // Convert a 12-bit value into a voltage.
00225 float MCP4822A::value2voltage( int value, int gain ) {
00226 
00227     float voltage = value * MCP4822_VREF * gain / 4096000.0;
00228     return voltage;
00229 }
00230 
00231 // Set latch signal to "enable".
00232 void MCP4822A::latch_enable() {
00233 
00234     // Latch all chips. There should be a delay of at least T_LS=40
00235     // nanoseconds between the last CS rising edge and the LDAC falling
00236     // edge. The software function calls seem to be sufficient to
00237     // introduce that delay. A delay may be inserted here if this
00238     // software is ported to a faster processor.
00239     if (_latched) _nldac->write(0);
00240     // The LDAC pulse width must be at least T_LD=100 nanoseconds long.
00241     // A delay can be inserted here if necessary, but so far this has
00242     // not been needed (see above).
00243     return;
00244 }
00245 
00246 // Set latch signal to "disable".
00247 void MCP4822A::latch_disable() {
00248 
00249     // Disable latch for all chips.
00250     if (_latched) _nldac->write(1);
00251     return;
00252 }
00253 
00254 // Shut down one chip.
00255 void MCP4822A::shdn( int dac ) {
00256 
00257     // Shut down one particular chip
00258     _ncs_array[dac]->write(0);
00259     _spi.write(MCP4822_REG_SHDN);
00260     _ncs_array[dac]->write(1);
00261     return;
00262 }
00263 
00264 // Shut down all chips.
00265 void MCP4822A::shdn_all( ) {
00266 
00267     // Shut down all chips
00268     int dac;
00269     for (dac=0; dac<_ndacs; dac++) {
00270         shdn( dac );
00271     }
00272     latch_disable();
00273     return;
00274 }