Diff: MCP4922.cpp

Revision:

0:5737b1972549

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MCP4922.cpp	Wed May 11 12:04:37 2011 +0000
@@ -0,0 +1,156 @@
+/*
+ * MCP4922 - DAC library.
+ */
+
+#include "mbed.h"
+#include "MCP4922.h"
+
+using namespace mbed;
+
+int dac =0;
+
+MCP4922::MCP4922(PinName mosi, PinName sclk, PinName cs) : _spi(mosi, NC, sclk) {
+
+    int i;
+    _ndacs = 1;
+    _ncs_array = new DigitalOut*[ _ndacs ];
+    for (i=0; i<_ndacs; i++) {
+        _ncs_array[i] = new DigitalOut(cs);
+    }
+
+    // Initialise the DAC SPI interface.
+    _init();
+}
+
+// Destructor
+MCP4922::~MCP4922() {
+
+    // 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 MCP4922::_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 MCP4922::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 MCP4922::writeA(int value) {
+
+    // Set up the command register with the appropriate value.
+    // For efficiency, the caller is assumed to have checked dac.
+    int reg;
+    //int dac = 0;
+    reg = (value & 0x0FFF) | MCP4922_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 B with gain 1.
+void MCP4922::writeB(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) | MCP4922_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 an array of values to the DACs.
+void MCP4922::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;
+
+        for (i=0; i<nchans;) {
+            dac = i/2;
+            writeA(values[i]);
+            i++;
+            if (i < nchans) {
+                writeB(values[i]);
+                i++;
+            } else break;
+        }
+
+    // Automatically latch the new voltages if the latch flag is 1.
+    if (latch && _latched)
+        latch_enable();
+    return;
+}
+
+// Set latch signal to "enable".
+void MCP4922::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 MCP4922::latch_disable() {
+
+    // Disable latch for all chips.
+    if (_latched) _nldac->write(1);
+    return;
+}
+