Steven Beard
Write to a daisy chained array of MCP4822 DAC chips, with latching.
Dependents: MCP4822_demo MCP4822_SinewaveV2
Diff: MCP4822A.h
- Revision:
- 0:fcd6f2777ddd
diff -r 000000000000 -r fcd6f2777ddd MCP4822A.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/MCP4822A.h Tue Feb 22 17:23:08 2011 +0000
@@ -0,0 +1,253 @@
+/*
+ * 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"
+
+#ifndef MCP4822_H
+#define MCP4822_H
+
+/* Reference: Microchip Technology (2005), MCP4821/MCP4822 DAC Data Sheet. */
+
+// MCP4822 reference voltage.
+#define MCP4822_VREF 2048 // Reference voltage (mV)
+
+/* Define possible combinations of 16-bit command register bits */
+#define MCP4822_REG_A1 0x3000 // Channel A gain 1
+#define MCP4822_REG_A2 0x1000 // Channel A gain 2
+#define MCP4822_REG_B1 0xB000 // Channel B gain 1
+#define MCP4822_REG_B2 0x9000 // Channel B gain 2
+#define MCP4822_REG_SHDN 0x0000 // Output power down
+
+/*+
+ * Interface to an array of MCP4822 12-bit dual-output DACs daisy chained
+ * on an SPI bus, with each DAC selected using an array of DigitalOut pins.
+ * All the DACs may be latched together using a common nLDAC pin.
+ *
+ * +-----------------------------------+
+ * |+------------------------+ |
+ * ||+-------------+ | |
+ * ||| nCS1 nCS2 nCS3
+ * +--+++-+ | | |
+ * | | +-+----+ +-+----+ +-+----+
+ * | mbed +---SPI---+ DAC1 +--+ DAC2 +--+ DAC3 +--etc...
+ * | | +-+----+ +-+----+ +-+----+
+ * +---+--+ | | |
+ * | nLDAC nLDAC nLDAC
+ * +--------------+---------+---------+
+ *-
+ */
+class MCP4822A {
+public:
+ /*+
+ * Constructor: MCP4822A
+ *
+ * Description:
+ * A class which describes an array of MCP4822 DACs connected in
+ * a daisy chain with an SPI interface. Each DAC is selected using
+ * its own separate "not CS" pin and all the DACs may be latched
+ * together using a single "not LDAC" pin.
+ *
+ * Parameters:
+ * ndacs, int
+ * The number of DAC chips included in the array. Must be at
+ * least 1. (Limited by the number of "not CS" pins available.)
+ * mosi, PinName
+ * The SPI data out pin.
+ * sclk, PinName
+ * The SPI clock pin.
+ * ncslist, PinName[]
+ * An array of "not chip select" ("not CS") pins - one per DAC
+ * chip. Each pin is held low to make the DAC respond to SPI
+ * input. The array must contain at least ndacs elements (only
+ * the first ndacs elements will be used).
+ * nldac, PinName (optional)
+ * The "not latch DAC" ("not LDAC") pin. Setting this pin low
+ * causes each DAC to apply the preset A and B voltages to its
+ * outputs. The pin is optional. The DAC will apply new voltages
+ * immediately if the "not LDAC" pin is held permanently to
+ * ground. This parameter is optional, and if not given will be
+ * assumed NC (not connected).
+ *-
+ */
+ MCP4822A ( int ndacs, PinName mosi, PinName sclk, PinName ncslist[], PinName nldac=NC );
+
+ /*+
+ * Destructor: MCP4822A
+ *-
+ */
+ ~MCP4822A();
+
+ /*+
+ * frequency: Set the SPI bus clock frequency in Hz.
+ *
+ * Parameters:
+ * freq, int
+ * The SPI bus frequency in Hz. Must be within the range
+ * supported by both the SPI interface and the DAC chips
+ * (~10 KHz to 20 MHz).
+ *-
+ */
+ void frequency( int freq );
+
+ /*+
+ * writeA1: Write 12-bit data to channel A with gain set to 1.
+ * writeA2: Write 12-bit data to channel A with gain set to 2.
+ * writeB1: Write 12-bit data to channel B with gain set to 1.
+ * writeB2: Write 12-bit data to channel B with gain set to 2.
+ *
+ * These functions will automatically select the chip with the "not CS"
+ * signal. If the "not LDAC" pin is used, it is up to the caller to
+ * enable or disable that signal. For example:
+ *
+ * latch_disable();
+ * writeA2( 1500 );
+ * latch_enable();
+ *
+ * Choose these functions when high performance is most important.
+ *
+ * Parameters:
+ * dac, int
+ * The DAC chip to be addressed, corresponding to the elements
+ * of the ncslist[] array used to create the MCP4822A object.
+ * Must be in the range 0 to ndacs-1.
+ * value, int
+ * The number to be written to the 12 data bits of the A or B
+ * register of the DAC chip. At a gain setting of 2, this value
+ * corresponds to a voltage demand in millivolts. Only the first
+ * 12 bits are used, so the value will wrap around after 4095.
+ * (Note: Strictly this should be an unsigned int, but the SPI
+ * interface library expects an int.)
+ *-
+ */
+ void writeA1( int dac, int value );
+ void writeA2( int dac, int value );
+ void writeB1( int dac, int value );
+ void writeB2( int dac, int value );
+
+ /*+
+ * write: Write an array of 12-bit register values to multiple DAC channels.
+ *
+ * Choose this function when flexibility and convenience are most important.
+ *
+ * Parameters:
+ * nchans, int
+ * The number of channels to be written. There are two channels
+ * per DAC, so this value must lie between 2 and ndacs x 2.
+ * values, int[]
+ * An array of values to be written to the 12 data bits of the DAC
+ * registers, in the order dac/chan = 0/A, 0/B, 1/A, 1/B, etc...
+ * The array must contain at least nchans elements (but only the
+ * first nchans elements will be used for longer arrays).
+ * At a gain setting of 2, these values corresponds to a voltage
+ * demand in millivolts. They will wrap back to 0 above 4095.
+ * (Note: Strictly this should be an unsigned int array, but the SPI
+ * interface library expects an int.)
+ * gain, int (optional)
+ * The required gain setting (1 or 2). If not specified, a default
+ * of 2 will be assumed.
+ * latch, int (optional)
+ * A flag set to 1 if the "not LDAC" signal should be latched after
+ * setting up the array of voltages. If not specified, a default
+ * of 1 will be assumed.
+ *-
+ */
+ void write( int nchans, int values[], int gain=2, int latch=1 );
+
+ /*+
+ * voltage2value - convert a voltage into a 12-bit data value.
+ *
+ * Parameters:
+ * voltage, float
+ * The voltage to be converted (in volts). The sign is ignored.
+ * gain, int (optional)
+ * The gain setting required (1 or 2). If not specified, a default
+ * of 2 will be assumed.
+ *
+ * Returns:
+ * value, int.
+ * The 12-bit data value corresponding to the given
+ * voltage. 4095 will be returned for out of range
+ * voltages.
+ *-
+ */
+ int voltage2value( float voltage, int gain=2 );
+
+ /*+
+ * value2voltage - convert a 12-bit data value into a voltage.
+ *
+ * Parameters:
+ * value, int
+ * The 12-bit data value to be converted to a voltage.
+ * gain, int (optional)
+ * The gain setting required (1 or 2). If not specified, a default
+ * of 2 will be assumed.
+ *
+ * Returns:
+ * voltage, float.
+ * The voltage (in volts) corresponding the the given 12-bit
+ * data value at the given gain setting.
+ *-
+ */
+ float value2voltage( int value, int gain=2 );
+
+ /*+
+ * latch_enable: enable the latch signal - the DAC(s) will apply
+ * voltage demands.
+ *
+ * latch_disable: disable the latch signal - the DAC(s) will not
+ * apply voltage demands.
+ *
+ * These functions only apply for objects constructed with the
+ * optional nldac parameter assigned to a pin.
+ *-
+ */
+ void latch_enable();
+ void latch_disable();
+
+ /*+
+ * shdn: Shut down a DAC. It will sleep until woken by a new command
+ * over the SPI bus.
+ *-
+ */
+ void shdn(int dac);
+ void shdn_all();
+
+private:
+ // Make copy constructor private to prevent the object being copied.
+ // The pins are available to one and only one object.
+ MCP4822A( const MCP4822A& rhs );
+
+ /* Initialise the DAC interface. */
+ void _init();
+
+ int _ndacs; // The number of DACS in the array
+ int _latched; // Is the "not LDAC" pin used (1=yes; 0=no)?
+ SPI _spi; // SPI bus object for communicating with DAC.
+ DigitalOut** _ncs_array; // Array of pointers to DigitalOut objects
+ // connected to "not CS" pins.
+ DigitalOut* _nldac; // Pointer to DigitalOut object connected
+ // to "not LDAC" pin (if any - NULL if none).
+};
+
+#endif