Diff: MCP4822A.cpp

Revision:

0:fcd6f2777ddd

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MCP4822A.cpp	Tue Feb 22 17:23:08 2011 +0000
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+/*
+ * MCP4822A - DAC array library.
+ *
+ * Copyright (c) 2011 Steven Beard, UK Astronomy Technology Centre.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "mbed.h"
+#include "MCP4822A.h"
+
+using namespace mbed;
+
+/*+
+ * Interface to an array of MCP4822 12-bit dual-output DACs daisy chained
+ * on an SPI bus and selected using DigitalOut pins.
+ *
+ * For a detailed API description see MCP4822.h.
+ *-
+ */
+// Constructor
+MCP4822A::MCP4822A(int ndacs, PinName mosi, PinName sclk, PinName ncslist[], PinName nldac) : _spi(mosi, NC, sclk) {
+
+    // Create an array of DigitalOut objects connected to each NCS pin.
+    int i;
+    _ndacs = (ndacs > 0) ? ndacs : 1;
+    _ncs_array = new DigitalOut*[ _ndacs ];
+    for (i=0; i<_ndacs; i++) {
+        _ncs_array[i] = new DigitalOut( ncslist[i] );
+    }
+
+    // The LDAC pin is optional.
+    if (nldac == NC) {
+        // LDAC is not connected for this DAC.
+        _latched = 0;
+        _nldac = NULL;
+    } else {
+        // LDAC is connected - create a DigitalOut object connected to it.
+        _latched = 1;
+        _nldac = new DigitalOut( nldac );
+    }
+
+    // Initialise the DAC SPI interface.
+    _init();
+}
+
+// Destructor
+MCP4822A::~MCP4822A() {
+
+    // Before destroying the object, shut down all the chips.
+    shdn_all();
+
+    // Delete all the NCS DigitalOut objects and the array pointing to
+    // them.
+    int i;
+    for (i=0; i<_ndacs; i++) {
+        delete _ncs_array[i];
+    }
+    delete [] _ncs_array;
+
+    // Delete the LDAC DigitalOut object if it exists.
+    if (_latched ) delete _nldac;
+}
+
+// Initialise SPI interface.
+void MCP4822A::_init() {
+
+    // Set up the SPI for 16-bit values (12-bit + 4 command bits) and mode 0.
+    _spi.format(16, 0);
+
+    // Start with all the CS and LDAC signals high (disabled)
+    int i;
+    for (i=0; i<_ndacs; i++) {
+        _ncs_array[i]->write(1);
+    }
+
+    if (_latched ) _nldac->write(1);
+    return;
+}
+
+// Set SPI clock frequency.
+void MCP4822A::frequency( int freq ) {
+
+    // Set the SPI interface clock frequency in Hz.
+    _spi.frequency( freq );
+    return;
+}
+
+/*
+ * Note: There is a lot of code in common between the following 4 functions.
+ * The code is kept in line to keep it efficient. Could the functions have
+ * been written as templates?
+ */
+// Write to DAC channel A with gain 1.
+void MCP4822A::writeA1(int dac, int value) {
+
+    // Set up the command register with the appropriate value.
+    // For efficiency, the caller is assumed to have checked dac.
+    int reg;
+    reg = (value & 0x0FFF) | MCP4822_REG_A1;
+
+    // Select the DAC chip, write to its command register and
+    // then unselect the DAC chip.
+    _ncs_array[dac]->write(0);
+    _spi.write(reg);
+    _ncs_array[dac]->write(1);
+    return;
+}
+
+// Write to DAC channel A with gain 2.
+void MCP4822A::writeA2(int dac, int value) {
+
+    // Set up the command register with the appropriate value.
+    // For efficiency, the caller is assumed to have checked dac.
+    int reg;
+    reg = (value & 0x0FFF) | MCP4822_REG_A2;
+
+    // Select the DAC chip, write to its command register and then
+    // unselect the DAC chip.
+    _ncs_array[dac]->write(0);
+    _spi.write(reg);
+    _ncs_array[dac]->write(1);
+    return;
+}
+
+// Write to DAC channel B with gain 1.
+void MCP4822A::writeB1(int dac, int value) {
+
+    // Set up the command register with the appropriate value.
+    // For efficiency, the caller is assumed to have checked dac.
+    int reg;
+    reg = (value & 0x0FFF) | MCP4822_REG_B1;
+
+    // Select the DAC chip, write to its command register and then
+    // unselect the DAC chip.
+    _ncs_array[dac]->write(0);
+    _spi.write(reg);
+    _ncs_array[dac]->write(1);
+    return;
+}
+
+// Write to DAC channel B with gain 2.
+void MCP4822A::writeB2(int dac, int value) {
+
+    // Set up the command register with the appropriate value.
+    // For efficiency, the caller is assumed to have checked dac.
+    int reg;
+    reg = (value & 0x0FFF) | MCP4822_REG_B2;
+
+    // Select the DAC chip, write to its command register and then
+    // unselect the DAC chip.
+    _ncs_array[dac]->write(0);
+    _spi.write(reg);
+    _ncs_array[dac]->write(1);
+    return;
+}
+
+// Write an array of values to the DACs.
+void MCP4822A::write(int nchans, int values[], int gain, int latch) {
+
+    // nchans must be at least 1 but less than or equal to ndacs x 2.
+    if (nchans < 1) nchans = 1;
+    const int maxchans = _ndacs * 2;
+    if (nchans > maxchans) nchans = maxchans;
+
+    if (latch && _latched)
+        latch_disable();
+
+    int i, dac;
+    if ( gain == 2 ) {
+
+        for (i=0; i<nchans;) {
+            dac = i/2;
+            writeA2(dac, values[i]);
+            i++;
+            if (i < nchans) {
+                writeB2(dac, values[i]);
+                i++;
+            } else break;
+        }
+    } else {
+
+        for (i=0; i<nchans;) {
+            dac = i/2;
+            writeA1(dac, values[i]);
+            i++;
+            if (i < nchans) {
+                writeB1(dac, values[i]);
+                i++;
+            } else break;
+        }
+    }
+
+    // Automatically latch the new voltages if the latch flag is 1.
+    if (latch && _latched)
+        latch_enable();
+    return;
+}
+
+// Convert a voltage into a 12-bit value.
+int MCP4822A::voltage2value( float voltage, int gain ) {
+
+    int value = int(4096000.0 * abs(voltage) / float(MCP4822_VREF * gain));
+    if ( value > 0x0FFF ) value = 0x0FFF;
+    return value;
+}
+
+// Convert a 12-bit value into a voltage.
+float MCP4822A::value2voltage( int value, int gain ) {
+
+    float voltage = value * MCP4822_VREF * gain / 4096000.0;
+    return voltage;
+}
+
+// Set latch signal to "enable".
+void MCP4822A::latch_enable() {
+
+    // Latch all chips. There should be a delay of at least T_LS=40
+    // nanoseconds between the last CS rising edge and the LDAC falling
+    // edge. The software function calls seem to be sufficient to
+    // introduce that delay. A delay may be inserted here if this
+    // software is ported to a faster processor.
+    if (_latched) _nldac->write(0);
+    // The LDAC pulse width must be at least T_LD=100 nanoseconds long.
+    // A delay can be inserted here if necessary, but so far this has
+    // not been needed (see above).
+    return;
+}
+
+// Set latch signal to "disable".
+void MCP4822A::latch_disable() {
+
+    // Disable latch for all chips.
+    if (_latched) _nldac->write(1);
+    return;
+}
+
+// Shut down one chip.
+void MCP4822A::shdn( int dac ) {
+
+    // Shut down one particular chip
+    _ncs_array[dac]->write(0);
+    _spi.write(MCP4822_REG_SHDN);
+    _ncs_array[dac]->write(1);
+    return;
+}
+
+// Shut down all chips.
+void MCP4822A::shdn_all( ) {
+
+    // Shut down all chips
+    int dac;
+    for (dac=0; dac<_ndacs; dac++) {
+        shdn( dac );
+    }
+    latch_disable();
+    return;
+}