Section 33. Audio Digital-to-Analog Converter (DAC)
HIGHLIGHTS
This section of the manual contains the following major topics:
© 2009 Microchip Technology Inc.
DS70211B-page 33-1
33
Audio
Digital-to-Analog
Converter (DAC)
33.1 Introduction .................................................................................................................. 33-2
33.2 Key Features................................................................................................................ 33-3
33.3 DAC Registers ............................................................................................................. 33-3
33.4 Module Operation ........................................................................................................ 33-7
33.5 Interrupts and Status .................................................................................................. 33-10
33.6 Audio DAC Operation without DMA ........................................................................... 33-11
33.7 Audio DAC Operation with DMA ................................................................................ 33-13
33.8 External Circuit Example............................................................................................ 33-16
33.9 Operations in Power-Saving Modes .......................................................................... 33-17
33.10 Register Map.............................................................................................................. 33-18
33.11 Related Application Notes.......................................................................................... 33-19
33.12 Revision History ......................................................................................................... 33-20
dsPIC33F Family Reference Manual
33.1
INTRODUCTION
The Audio Digital-to-Analog Converter (DAC) module is a 16-bit Delta-Sigma signal converter
designed for audio applications. Two output channels support stereo operations. Data input is in
the form of a 16-bit digital value from the application program via the DMA module or the DAC
data and control registers. Data output is an analog voltage, which is proportional to the digital
input value.
Each output channel provides three voltage outputs:
• Positive DAC output
• Negative DAC output
• Midpoint voltage output (not present on all devices)
The midpoint output is an offset voltage level that represents the midpoint of the output voltage
range.
Figure 33-1 is a simplified block diagram of the Audio DAC. A four-word deep FIFO buffers the
data input for each channel. If at any time the FIFO becomes empty (for example, if the DMA
module or processor cannot provide data in a timely manner), the DAC accepts alternate data
from the DAC Default Data Register (DACxDFLT). This register provides a default input value
that represents a “safe” output voltage, which is often the midpoint value or a zero value.
The sample rate of the DAC is established by an integer division of the rate of an auxiliary
oscillator or system clock by a divider circuit. The divisor ratio is specified by the DAC Clock
Divider (DACFDIV<6:0>) Configuration bits in the DAC Control Register (DACxCON).
Figure 33-1:
Audio DAC Module Block Diagram
Right Channel
FIFO
DAC1RM
DACxRDAT
D/A
Amp
DAC1RP
DAC1RN
16-bit Data Bus
Note 1
ACLK
CONTROL
DACFDIV
CLK DIV
DACxDFLT
DAC1LM
FIFO
D/A
Amp
DAC1LP
DAC1LN
DACxLDAT
Note 1
Left Channel
Note
DS70211B-page 33-2
1:
If FIFO is empty, data will be taken from the DACxDFLT register.
© 2009 Microchip Technology Inc.
Section 33. Audio Digital-to-Analog Converter (DAC)
33.2
KEY FEATURES
The Audio DAC provides these key features:
•
•
•
•
•
•
•
•
•
16-bit resolution (14-bit accuracy)
Second-order digital Delta-Sigma modulator
256x oversampling ratio
100 ksps maximum sampling rate
User controllable sample clock
Maximum input signal frequency of 45 kHz
Differential analog outputs
Four word deep input buffer
16-bit processor I/O and DMA interfaces
Note:
33.3
The Audio DAC module is designed specifically for the Audio applications. Using
this module for control loop type of applications is not recommended.
DAC REGISTERS
The Audio DAC module is controlled by five DAC registers.
• DACxCON: DAC Control Register
This register configures the corresponding DAC module by enabling/disabling the module
and by specifying data format, DAC filter clock divider and operations in Idle/Sleep mode.
33
• DACxSTAT: DAC Status and Control Register
• DACxDFLT: DAC Default Data Register
This register specifies a DAC default value to be used as the input when the FIFO is empty.
• DACxLDAT: DAC Left Channel Data Register
This register specifies data for the left channel.
• DACxRDAT: DAC Right Channel Data Register
This register specifies data for the right channel.
© 2009 Microchip Technology Inc.
DS70211B-page 33-3
Audio
Digital-to-Analog
Converter (DAC)
This register specifies which channels are enabled and the status of the data buffer of that
channel.
dsPIC33F Family Reference Manual
Register 33-1:
DACxCON: DAC Control Register
R/W-0
U-0
R/W-0
R/W-0
U-0
U-0
U-0
R/W-0
DACEN
—
DACSIDL
AMPON
—
—
—
FORM
bit 15
bit 8
U-0
R/W-0
R/W-0
—
R/W-0
R/W-0
R/W-1
R/W-0
R/W-1
DACFDIV<6:0>
bit 7
bit 0
Legend:
R = Readable bit
W = Writable bit
U = Unimplemented bit, read as ‘0’
-n = Value at POR
‘1’ = Bit is set
‘0’ = Bit is cleared
x = Bit is unknown
bit 15
DACEN: DAC Enable bit
1 = Enables module
0 = Disables module
bit 14
Unimplemented: Read as ‘0’
bit 13
DACSIDL: Stop in Idle Mode bit
1 = Discontinue module operation when device enters Idle mode
0 = Continue module operation in Idle mode
bit 12
AMPON: Enable Analog Output Amplifier in Sleep Mode/Stop-in Idle Mode bit
1 = Analog Output Amplifier is enabled during Sleep Mode/Stop-in Idle mode
0 = Analog Output Amplifier is disabled during Sleep Mode/Stop-in Idle mode. All channels are reset
bit 11-9
Unimplemented: Read as ‘0’
bit 8
FORM: Data Format Select bit
1 = Signed integer
0 = Unsigned integer
bit 7
Unimplemented: Read as ‘0’
bit 6-0
DACFDIV<6:0>: DAC Clock Divider bits
1111111 = Divide input clock by 128
•
•
•
•
0000101 = Divide input clock by 6 (default)
•
•
•
•
0000010 = Divide input clock by 3
0000001 = Divide input clock by 2
0000000 = Divide input clock by 1 (no divide)
DS70211B-page 33-4
© 2009 Microchip Technology Inc.
Section 33. Audio Digital-to-Analog Converter (DAC)
Register 33-2:
DACxSTAT: DAC Status and Control Register
R/W-0
U-0
R/W-0
U-0
U-0
R/W-0
R-0
R-0
LOEN
—
LMVOEN
—
—
LITYPE
LFULL
LEMPTY
bit 15
bit 8
R/W-0
U-0
R/W-0
U-0
U-0
R/W-0
R-0
R-0
ROEN
—
RMVOEN
—
—
RITYPE
RFULL
REMPTY
bit 7
bit 0
Legend:
R = Readable bit
W = Writable bit
U = Unimplemented bit, read as ‘0’
-n = Value at POR
‘1’ = Bit is set
‘0’ = Bit is cleared
LOEN: Left Channel DAC Output Enable bit
1 = Positive and negative DAC outputs are enabled
0 = DAC outputs are disabled
bit 14
Unimplemented: Read as ‘0’
bit 13
LMVOEN: Left Channel Midpoint DAC Output Voltage Enable bit
1 = Midpoint DAC output is enabled
0 = Midpoint output is disabled
bit 12-11
Unimplemented: Read as ‘0’
bit 10
LITYPE: Left Channel Type of Interrupt bit
1 = Interrupt if FIFO is empty
0 = Interrupt if FIFO is not full
bit 9
LFULL: Status, Left Channel Data Input FIFO is Full bit
1 = FIFO is full
0 = FIFO is not full
bit 8
LEMPTY: Status, Left Channel Data Input FIFO is Empty bit
1 = FIFO is empty
0 = FIFO is not empty
bit 7
ROEN: Right Channel DAC Output Enable bit
1 = Positive and negative DAC outputs are enabled
0 = DAC outputs are disabled
bit 6
Unimplemented: Read as ‘0’
bit 5
RMVOEN: Right Channel Midpoint DAC Output Voltage Enable bit
1 = Midpoint DAC output is enabled
0 = Midpoint output is disabled
bit 4-3
Unimplemented: Read as ‘0’
bit 2
RITYPE: Right Channel Type of Interrupt bit
1 = Interrupt if FIFO is empty
0 = Interrupt if FIFO is not full
bit 1
RFULL: Status, Right Channel Data Input FIFO is Full bit
1 = FIFO is full
0 = FIFO is not full
bit 0
REMPTY: Status, Right Channel Data Input FIFO is Empty bit
1 = FIFO is empty
0 = FIFO is not empty
© 2009 Microchip Technology Inc.
33
Audio
Digital-to-Analog
Converter (DAC)
bit 15
x = Bit is unknown
DS70211B-page 33-5
dsPIC33F Family Reference Manual
Register 33-3:
DACxDFLT: DAC Default Data Register
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
DACDFLT<15:8>
bit 15
bit 8
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
DACDFLT<7:0>
bit 7
bit 0
Legend:
R = Readable bit
W = Writable bit
U = Unimplemented bit, read as ‘0’
-n = Value at POR
‘1’ = Bit is set
‘0’ = Bit is cleared
bit 15-0
x = Bit is unknown
DACDFLT: DAC Default Value bits
Register 33-4:
DACxLDAT: DAC Left Channel Data Register
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
DACLDAT<15:8>
bit 15
bit 8
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
DACLDAT<7:0>
bit 7
bit 0
Legend:
R = Readable bit
W = Writable bit
U = Unimplemented bit, read as ‘0’
-n = Value at POR
‘1’ = Bit is set
‘0’ = Bit is cleared
bit 15-0
x = Bit is unknown
DACLDAT: Left Channel Data bits
Register 33-5:
DACxRDAT: DAC Right Channel Data Register
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
DACRDAT<15:8>
bit 15
bit 8
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
R/W-0
DACRDAT<7:0>
bit 7
bit 0
Legend:
R = Readable bit
W = Writable bit
U = Unimplemented bit, read as ‘0’
-n = Value at POR
‘1’ = Bit is set
‘0’ = Bit is cleared
bit 15-0
x = Bit is unknown
DACRDAT: Right Channel Data bits
DS70211B-page 33-6
© 2009 Microchip Technology Inc.
Section 33. Audio Digital-to-Analog Converter (DAC)
33.4
MODULE OPERATION
Figure 33-2 illustrates the digital-to-analog conversion process. The digital interpolation filter
up-samples the input signal to create additional interpolated data points. The over-sampling ratio
is 256:1, or 256x the incoming sampling rate. For example, a 100 ksps input signal (the maximum
sampling rate) produces 25.6M data points per second.
The interpolation filter also eliminates unwanted noise produced by the up-sampling process.
The output of the interpolation filter drives the Sigma-Delta modulator, which converts the word
output from the interpolation filter into a serial bit stream.
The bit stream from the modulator is processed by the reconstruction filter to convert the bit
stream to an analog signal. It then performs a low-pass filter to yield the desired voltage levels.
The reconstruction filter produces two differential voltage outputs and a midpoint reference:
• Positive (voltage level representing the output signal)
• Negative (complement of the positive output signal voltage level)
• Midpoint (offset voltage level representing the midpoint of the output voltage range)
Figure 33-2:
Block Diagram of Digital-to-Analog Process
CPU
DACR Interrupt
DACxRDAT
FIFO
DAC1RM
256*Fs
Interpolation
Filter (256)
Sigma-Delta
Modulator
Reconstruction
Filter
Analog
Amplifier
DAC1RP
DA1CRN
Right Channel Digital-to-Analog Converter
ACLK
CLK DIV
DACCLK = Fs x 256
DACxDFLT
DAC1LM
DACFDIV<6:0>
Fs
256*Fs
Interpolation
Filter (256)
Sigma-Delta
Modulator
Reconstruction
Filter
Analog
Amplifier
DAC1LP
DAC1LN
Left Channel Digital-to-Analog Converter (DAC)
DACxLDAT
FIFO
DACL Interrupt
CPU
© 2009 Microchip Technology Inc.
DS70211B-page 33-7
Audio
Digital-to-Analog
Converter (DAC)
Fs
33
dsPIC33F Family Reference Manual
33.4.1
Data Format
The DAC module accepts 16-bit input data in two formats. Data formatting is controlled by the
Data Format Select (FORM) bit in the DAC Control (DACxCON<8>) register. The supported
formats are:
• 1 = Signed (2’s complement)
• 0 = Unsigned
If the FORM bit is configured for unsigned data (FORM = 0), the user input data yields the
following behavior:
•
•
•
•
0xFFFF = Most positive output voltage
0x8000 = Midpoint output voltage
0x7FFF = Value just below midpoint
0x0000 = Minimum output voltage
If the FORM bit is configured for signed data (FORM = 1), the user input data yields the following
behavior:
•
•
•
•
0x7FFF = Most positive output voltage
0x0000 = Midpoint output voltage
0xFFFF = Value just below midpoint
0x8000 = Minimum output voltage
33.4.2
Clock
The DAC clock (DACCLK) must be equal to the sampling rate times 256. Assuming a 100 ksps
input, the DAC clock rate must be 25.6 MHz (100,000 x 256 = 25,600,000).
DACCLK is generated by dividing the high-speed oscillator (auxiliary or system clock) by a
specified value. The divisor ratio is specified by clock divider bits (DACFDIV<6:0>) in the DAC
Control (DACxCON register<6:0>). The resulting DACCLK must not exceed 25.6 MHz.
Consider an application example where the dsPIC® DSC device uses the device FRC as the
clock source. The device oscillator pre-PLL divider (N1) and post-PLL divider (N2) are set to
divide by 2. For more details on oscillator selection, refer to Section 39. “Oscillator (Part III)”
(DS70216). It is desired that the DAC module be configured to output a 8 kHz sampled signal.
Therefore, the DAC clock rate must be 256 x 8 kHz = 2.048 MHz.
For this example, the dsPIC DSC PLL can be configured to provide a system clock, which is an
integral multiple of the DAC clock rate (i.e., 2.048 MHz). The system clock source to the DAC
module is designated FVCO and is the output of the PLL before the post-PLL divider (N2). For
more details, refer to Figure 39-8: PLL Block Diagram in Section 39. “Oscillator
(Part III)” (DS70216). By selecting the value of M to be 40, FVCO is given as shown in
Equation 33-1:
Equation 33-1:
FVCO Equation
FVCO = (7.3728 * 106 * 40)/2 = 147.456 * 106 MHz
This FVCO value is an integral multiple (2.048 MHz x 72 = 147.456 x 106 MHz) of the required
DAC clock value. Setting the SELACLK (ACLKCON<13>) bit to ‘0’ and setting the DACFDIV
register value to divide the FVCO clock by 72 will produce the desired DAC clock.
DS70211B-page 33-8
© 2009 Microchip Technology Inc.
Section 33. Audio Digital-to-Analog Converter (DAC)
Table 33-1 lists the DACCLK rates required to achieve common audio sample rates.
Table 33-1:
CLOCK RATE RATIO
DACCLK Rate (MHz)
(FS x 256)
Sample Data Rate (kHz)
(FS)
1.8432
7.2
2.048
8.0
2.4576
9.6
2.8224
11.025
4.096
16
5.6448
22.05
6.144
24
8.192
32
11.2896
44.1
12.288
48
22.5792
88.2
24.576
96.0
25.6
100
The DACCLK rate is achieved by selecting an Auxiliary Oscillator with the appropriate
DACFDIV<6:0> Configuration bits. For example, a DACCLK rate of 25.6 MHz (for 100 ksps input
rate) might be obtained as shown in Table 33-2:
Auxiliary Oscillator Frequency
Auxiliary Oscillator Frequency
DACFDIV Configuration Bits
25.6 MHz
DACFDIV = 0b0000000
51.2 MHz
DACFDIV = 0b0000001
76.8 MHz
DACFDIV = 0b0000010
For more details on oscillator selection, refer to Section 39. “Oscillator (Part III)” (DS70216).
© 2009 Microchip Technology Inc.
DS70211B-page 33-9
Audio
Digital-to-Analog
Converter (DAC)
Table 33-2:
33
dsPIC33F Family Reference Manual
33.5
INTERRUPTS AND STATUS
The Audio DAC provides two interrupts, one for each channel. Depending on the setting of the
interrupt Configuration bits (LITYPE for the left channel and RITYPE for the right channel) in the
DAC Status Register (DACxSTAT), the DAC interrupt is triggered by either a “FIFO Empty” or
“FIFO Not Full” condition. The FIFO Empty interrupt can be used with the Audio DAC to maximize
throughput while minimizing the impact of interrupts on the CPU. The FIFO Empty interrupt is the
simplest and preferred interrupt method for use with DMA.
The FIFO Not Full interrupt is used in applications without DMA to minimize the occurrence of
DAC under run. This interrupt can also be used with DMA, but additional software support is
required.
The DAC Interrupt Service Routine (ISR) must clear its corresponding interrupt flags (DAC1LIF
and DAC1RIF in the IFS4 register).
Note:
The Audio DAC reads data from FIFO every 256 DAC clock cycles. DAC interrupts
occur once the data is read, depending on the status of the FIFO.
Each channel includes two status bits to indicate the status of its FIFO, as shown in Table 33-3:
Table 33-3:
Channel
Left
Interrupt Status Bits
Name(1)
Description
LFULL (DAC1STAT<9>)
Left channel FIFO is full
LEMPTY (DAC1STAT<8>) Left channel FIFO is empty
Right
RFULL (DAC1STAT<1>)
Right channel FIFO is full
REMPTY (DAC1STAT<0>) Right channel FIFO is empty
Note 1:
DS70211B-page 33-10
These bits can be read in software to confirm the FIFO status.
© 2009 Microchip Technology Inc.
Section 33. Audio Digital-to-Analog Converter (DAC)
33.6
AUDIO DAC OPERATION WITHOUT DMA
Example 33-1 demonstrates a typical configuration for the Audio DAC module. In this example,
the interrupts for both channels are set to occur every time the corresponding FIFO is not full.
When the DAC Enable (DACEN) bit in the DAC Control (DACxCON<15>) register gets set, DAC
interrupts are generated for both channels. Since the FIFO is initially empty, the first data value
is read from the DAC Default (DACxDFLT) register. For this example, the default is set to a
midpoint value of 0x8000.
Example 33-1:
DAC Operation without DMA
DAC1STATbits.ROEN = 1;
DAC1STATbits.LOEN = 1;
/* Right Channel DAC Output Enabled */
/* Left Channel DAC Output Enabled */
DAC1STATbits.RITYPE = 0;
DAC1STATbits.LITYPE = 0;
/* Right Channel Interrupt if FIFO is not Full */
/* Left Channel Interrupt if FIFO is not Full */
DAC1CONbits.AMPON = 0;
DAC1CONbits.DACFDIV = 0;
DAC1CONbits.FORM = 0;
/* Amplifier Disabled During Sleep and Idle Modes */
/* Divide Clock by 1 (Assumes Clock is 25.6MHz) */
/* Data Format is Unsigned */
DAC1DFLT = 0x8000;
/* Default value set to Midpoint when FORM = 0 */
IFS4bits.DAC1RIF = 0;
IFS4bits.DAC1LIF = 0;
/* Clear Right Channel Interrupt Flag */
/* Clear Left Channel Interrupt Flag */
IEC4bits.DAC1RIE = 1;
IEC4bits.DAC1LIE = 1;
/* Right Channel Interrupt Enabled */
/* Left Channel Interrupt Enabled */
DAC1CONbits.DACEN = 1;
/* DAC1 Module Enabled */
33
void__attribute__((interrupt, no_auto_psv))_DAC1LInterrupt(void)
{
IFS4bits.DAC1LIF = 0;
/* Clear Left Channel Interrupt Flag */
DAC1LDAT = MyDataL[0];
/* User Code to Write to FIFO Goes Here */
}
Figure 33-3 illustrates how the Audio DAC interacts with the application program to respond to
DAC interrupts and transfer data in a timely manner. This example shows a single-word transfer
per interrupt. Depending on your particular application, you could choose to write up to four
words per interrupt.
Note:
© 2009 Microchip Technology Inc.
A write to the FIFO is ignored, if the FIFO is full or if a write occurs before the DAC
is enabled.
DS70211B-page 33-11
Audio
Digital-to-Analog
Converter (DAC)
void__attribute__((interrupt, no_auto_psv))_DAC1RInterrupt(void)
{
IFS4bits.DAC1RIF = 0;
/* Clear Right Channel Interrupt Flag */
DAC1RDAT = MyDataR[0];
/* User Code to Write to FIFO Goes Here */
}
dsPIC33F Family Reference Manual
Figure 33-3:
Audio DAC Interaction without DMA
AUDIO DAC MODULE
A.
When DAC is initialized,
DAC Enable (DACEN)
bit is set. FIFO is not full,
so DAC interrupts are
generated for both
channels. Because
FIFOs have no data,
contents of DACDFLT
register is processed by
both DAC channels.
Right Channel
Output
Default
Value
DACRDAT
FIFO
dsPIC33F CPU
USER APPLICATION
Interrupt Service Routine (ISR)
D/A
DACDFLT
Left Channel
Application program
recognizes interrupt
request and begins
processing ISR.
Output
Default
Value
DACLDAT
FIFO
AUDIO DAC MODULE
B.
Interrupt Service Routine
(ISR) writes to DACRDAT
and DACLDAT.
Right Channel
Output
Default
Value
ISR
D/A
DACRDAT
FIFO
dsPIC33F CPU
USER APPLICATION
ISR
D/A
Transfer Data
DACDFLT
Left Channel
Output
Default
Value
DACLDAT
FIFO
Transfer Data
AUDIO DAC MODULE
C.
After 256 DAC clock
cycles, the D/A reads
data from FIFO.
As the D/A processing
occurs the DAC data
register status
becomes “not full”,
causing another DAC
interrupt to be
generated.
Right Channel
Output
First
Sample
DACRDAT
FIFO
This process repeats
until the application
program turns off the
DAC module (disables
DACEN).
DS70211B-page 33-12
USER APPLICATION
ISR
D/A
DACDFLT
DACLDAT
FIFO
Output
First
Sample
ISR
D/A
AUDIO DAC MODULE
The application
program transfers the
next word to the left and
right data registers.
This transfer is
completed before the
D/A requests the next
input word (i.e., before
it completes 256 DAC
clock cycles).
dsPIC33F CPU
Left Channel
Output
First
Sample
D.
ISR
D/A
Right Channel
DACRDAT
FIFO
dsPIC33F CPU
USER APPLICATION
ISR
D/A
Transfer Data
DACDFLT
Output
First
Sample
Left Channel
DACLDAT
FIFO
ISR
D/A
Transfer Data
© 2009 Microchip Technology Inc.
Section 33. Audio Digital-to-Analog Converter (DAC)
33.7
AUDIO DAC OPERATION WITH DMA
On some of the dsPIC33F devices, the DMA module can transfer data from the CPU to the Audio
DAC without CPU assistance. Refer to the specific dsPIC33F device data sheet to determine if
DMA is present on your particular device. For more details on the DMA module, refer to Section
22. “Direct Memory Access (DMA)” (DS70182).
When the Audio DAC module uses DMA, it requires one DMA channel for each DAC channel.
The DAC channel can be mapped to any available DMA channel. Interaction begins when the
DMA receives an interrupt from the Audio DAC. Depending on the setting of the interrupt
Configuration bits (LITYPE for the left channel and RITYPE for the right channel) in the DAC
Status Register (DACxSTAT), the DMA interrupt is triggered by either a “FIFO Empty” or “FIFO
Not Full” condition (see 33.5 “Interrupts and Status”).
33.7.1
DMA Channel to Peripheral Association Setup
The DMA channel needs to know which interrupt request to respond to and which peripheral
target address to write to for the Audio DAC. The interrupt is identified by the Interrupt Select
(IRQSEL<6:0>) bits in the DMA Channel x IRQ Request (DMAxREQ) register (in the DMA
module). The write address is identified by DMA Channel X Peripheral Address (DMAxPAD)
register (also in the DMA module).
Table 33-4 shows the values that should be written to associate a particular peripheral with a
given DMA channel.
Table 33-4:
DMA Channel to Peripheral Association
Peripheral to DMA
Association
DMAxPAD Register Values
to Write to Peripheral
DAC1 – Right Data Output
1001110
0x03F6 – DAC1RDAT
DAC1 – Left Data Output
1001111
0x03F8 – DAC1LDAT
33.7.2
DMA Code Setup
Example 33-2 illustrates code for a typical DAC configuration for DMA operation. In this example,
the interrupts are set to occur every time the FIFO is empty. When the DAC Enable (DACEN) bit
gets set, an interrupt is generated because the FIFO is initially empty. Since the FIFO is empty,
the first data value is read from the default register. In this case, the default value is zero.
Figure 33-4 illustrates how the Audio DAC interacts with the DMA module to respond to DAC
interrupts and transfer data in a timely manner. This example shows a single-word transfer per
interrupt.
© 2009 Microchip Technology Inc.
DS70211B-page 33-13
33
Audio
Digital-to-Analog
Converter (DAC)
DMAxREQ Register
IRQSEL<6:0> Bits
dsPIC33F Family Reference Manual
Example 33-2:
DAC Operation with DMA
/* DMA Code */
unsigned int RightBufferA[32]__attribute__((space(dma)));
unsigned int RightBufferB[32]__attribute__((space(dma)));
unsigned int LeftBufferA[32]__attribute__((space(dma)));
unsigned int LeftBufferB[32]__attribute__((space(dma)));
/* DMA Channel 0 set to DAC1RDAT */
DMA0CONbits.AMODE = 0;
/* Register Indirect with Post Increment */
DMA0CONbits.MODE = 2;
/* Continuous Mode with Ping-Pong Enabled */
DMA0CONbits.DIR = 1;
/* Ram-to-Peripheral Data Transfer */
DMA0PAD = (volatile unsigned int)&DAC1RDAT;
/* Point DMA to DAC1RDAT */
DMA0CNT = 31;
DMA0REQ = 78;
/* 32 DMA Request */
/* Select DAC1RDAT as DMA Request Source */
DMA0STA = __builtin_dmaoffset(RightBufferA);
DMA0STB = __builtin_dmaoffset(RightBufferB);
IFS0bits.DMA0IF = 0;
IEC0bits.DMA0IE = 1;
/* Clear DMA Interrupt Flag */
/* Set DMA Interrupt Enable Bit */
DMA0CONbits.CHEN = 1;
/* Enable DMA Channel 0 */
/* DMA Channel 1 set to DAC1LDAT */
DMA1CONbits.AMODE = 0;
/* Register Indirect with Post Increment */
DMA1CONbits.MODE = 2;
/* Continuous Mode with Ping-Pong Enabled */
DMA1CONbits.DIR = 1;
/* Ram-to-Peripheral Data Transfer */
DMA1PAD = (volatile unsigned int)&DAC1LDAT;
/* Point DMA to DAC1LDAT */
DMA1CNT = 31;
DMA1REQ = 79;
/* 32 DMA Request */
/* Select DAC1LDAT as DMA Request Source */
DMA1STA = __builtin_dmaoffset(LeftBufferA);
DMA1STB = __builtin_dmaoffset(LeftBufferB);
IFS0bits.DMA1IF = 0;
IEC0bits.DMA1IE = 1;
/* Clear DMA Interrupt Flag */
/* Set DMA Interrupt Enable Bit */
DMA1CONbits.CHEN = 1;
/* Enable DMA Channel 1 */
/* DAC1 Code */
DAC1STATbits.ROEN = 1;
DAC1STATbits.LOEN = 1;
/* Right Channel DAC Output Enabled */
/* Left Channel DAC Output Enabled */
DAC1STATbits.RITYPE = 1;
DAC1STATbits.LITYPE = 1;
/* Right Channel Interrupt if FIFO is Empty */
/* Left Channel Interrupt if FIFO is Empty */
DAC1CONbits.AMPON = 0;
/*
DAC1CONbits.DACFDIV = 0;
/*
DAC1CONbits.FORM = 0;
/*
DAC1CONbits.DACEN = 1;
/*
/* Rest of User Code Goes Here */
Amplifier is Disabled During Sleep/Idle Modes */
Divide Clock by 1 (Assumes Clock is 25.6MHz) */
Data Format is Unsigned */
DAC1 Module Enabled */
void__attribute__((interrupt, no_auto_psv))_DMA0Interrupt(void)
{
IFS0bits.DMA0IF = 0;
/* Clear DMA Channel 0 Interrupt Flag */
/* User Code to update Right Buffer in DMA*/
}
void__attribute__((interrupt, no_auto_psv))_DMA1Interrupt(void)
{
IFS0bits.DMA1IF = 0;
/* Clear DMA Channel 1 Interrupt Flag */
/* User Code to update Left Buffer in DMA */
}
DS70211B-page 33-14
© 2009 Microchip Technology Inc.
Section 33. Audio Digital-to-Analog Converter (DAC)
Figure 33-4:
Audio DAC Interaction with DMA
DMA MODULE
AUDIO DAC MODULE
A.
When DAC is initialized,
DAC Enable (DACEN) bit
is set. FIFO is empty, so
DAC generates DMA
Requests for both
channels. Because
FIFOs have no data,
contents of DACDFLT
register is processed by
both DAC channels.
Right Channel
Output
Default
Value
DACRDAT
FIFO
D/A
Right DATA 1 Buffer B
DMA
CHANNEL 1
Left Channel
|
DACLDAT
FIFO
|
Right DATA 1 Buffer A
Right DATA n
DMA
CHANNEL 0
DACDFLT
Output
Default
Value
DMA
CONTROLLER
Right DATA n
Left DATA 1
Buffer A
Left DATA n
D/A
Left DATA 1
Buffer B
Left DATA n
DMA MODULE
AUDIO DAC MODULE
B.
DMA fetches data word
from the Right Data
Buffer A and writes it to
the right DAC Data
(DACRDAT) register.
It then fetches a data
word from the Left Data
Buffer A and writes it to
the left DAC Data
(DACLDAT) register.
Output
Default
Value
DACRDAT
FIFO
D/A
Right DATA 1 Buffer B
DMA
CHANNEL 1
Left Channel
|
DACLDAT
FIFO
|
Right DATA 1 Buffer A
Right DATA n
DMA
CHANNEL 0
DACDFLT
Output
Default
Value
DMA
CONTROLLER
Right DATA n
Left DATA 1
Buffer A
Left DATA n
D/A
Left DATA 1
Buffer B
Left DATA n
DMA MODULE
AUDIO DAC MODULE
C.
After 256 DAC clock
cycles, the default word
has been processed by
both channels. The D/A
converters read the next
word from their
respective FIFO and
generate DMA Request
to fetch next samples.
Right Channel
Output
First
Sample
DACRDAT
FIFO
D/A
Output
First
Sample
DMA
CONTROLLER
Right DATA 1 Buffer B
DMA
CHANNEL 1
Left Channel
|
DACLDAT
FIFO
|
Right DATA 1 Buffer A
Right DATA n
DMA
CHANNEL 0
DACDFLT
Right DATA n
Left DATA 1
Buffer A
Left DATA n
D/A
Left DATA 1
Buffer B
Left DATA n
DMA MODULE
AUDIO DAC MODULE
D.
The next words are
fetched from DMA
memory.
This process continues,
fetching and processing
one word at a time in
each channel until the
application program
terminates data transfer.
Right Channel
Output
First
Sample
DACRDAT
FIFO
D/A
DACDFLT
Output
First
Sample
D/A
DMA
CONTROLLER
DMA
CHANNEL 0
DMA
CHANNEL 1
Left Channel
|
DACLDAT
FIFO
|
Right DATA 1 Buffer A
Right DATA n
Right DATA 1 Buffer B
Right DATA n
Left DATA 1
Buffer A
Left DATA n
Left DATA 1
Buffer B
Left DATA n
© 2009 Microchip Technology Inc.
33
DS70211B-page 33-15
Audio
Digital-to-Analog
Converter (DAC)
Simultaneously, the DAC
continues processing
DACDFLT.
Right Channel
dsPIC33F Family Reference Manual
33.8
EXTERNAL CIRCUIT EXAMPLE
Figure 33-5 shows a typical configuration for connecting a speaker with a single channel of the
Audio DAC module. This example uses the differential outputs of the Audio DAC and produces
a single-ended output using op amp differential amplifiers. The corresponding output is two times
the positive input.
Figure 33-5:
External Circuit Example
100 µF
RIGHT CHANNEL
10K
3.3V
Headphone Amplifier
1
10K
VDD
VOUT1
DAC1RP
-
0.1µF
2
10K
DAC1RN
1µF
+
VOUT2
BYP
VIN2
CLK
SHUTDN
3
MCP6022
10K
VIN1
4
VCC/2
10
9
8
1µF
100 µF
0.1µF
7
5
100K
6
UP/DN
GND
S1
3.3V
1
2
4
3
LM4811
S1
CLK
100K
3.3V
4
3
1
2
VOL UP/DN
LEFT CHANNEL
100K
10K
10K
DAC1LP
10K
DAC1LN
+
10K
MCP6022
VCC/2
DS70211B-page 33-16
© 2009 Microchip Technology Inc.
Section 33. Audio Digital-to-Analog Converter (DAC)
33.9
OPERATIONS IN POWER-SAVING MODES
The dsPIC33F family of devices has four power modes comprised of one normal (full-power)
mode and three power-saving modes invoked by the PWRSAV instruction. Depending on the
mode selected, entry into a power-saving mode may also affect the operation of the module.
When the Enable Analog Output Amplifier (AMPON) bit in the DAC Control (DACxCON<12>)
register is set, the analog circuitry and the analog output amplifier are powered on during Sleep
and Stop-in-Idle mode. This configuration keeps the analog output voltage at a known state
during Sleep and Stop-in-Idle modes. If the AMPON bit is cleared and the processor enters Sleep
mode or Stop-in-Idle mode, the analog circuitry is powered off and held in reset to reduce current
consumption. When the output amplifier is powered off, the analog output is in a high-impedance
state.
In Sleep mode, if the AMPON bit is cleared, the DAC internal state, including the FIFOs (except
the SFRs), is reset, the clocks are stopped and the output analog amplifier and associated
circuitry are powered down. If the AMPON bit is set, the DAC internal state and the SFRs are
maintained, the clocks are stopped and the output analog amplifier and associated circuitry
remain powered up.
If the Stop-in-Idle Mode (DACSIDL) bit in the DAC Control (DACxCON<13>) register is set when
Idle mode is entered, and if the AMPON bit is not set, the DAC internal state (except the SFRs)
is reset, the clocks are stopped and the output analog amplifier and associated circuitry is
powered down. If the AMPON bit is set, the DAC internal state and the SFRs are maintained, the
clocks are stopped and the output analog amplifier and associated circuitry remains powered up.
If DACSIDL is not set when Idle mode is entered, the DAC ignores Idle mode and continues
running.
Note:
© 2009 Microchip Technology Inc.
If AMPON = 1 and DACEN = 0, reading the FIFO will empty the FIFO.
DS70211B-page 33-17
33
Audio
Digital-to-Analog
Converter (DAC)
The DACEN bit (DACxCON<15>) is cleared when the device enters Sleep mode or Stop-in-Idle
mode, regardless of the status of AMPON bit. If the AMPON bit is set before the device enters
Sleep mode or Stop-in-Idle mode, the new data can be placed in the FIFOs upon exiting Sleep
or Stop-in-Idle. When the DAC is re-enabled, it continues the operation where it left off.
REGISTER MAP
A summary of the Audio DAC registers is provided in Table 33-5.
Table 33-5:
File Name
Audio DAC Register Map
Bit 15
Bit 14
Bit 13
Bit 12
Bit 11
Bit 10
Bit 9
Bit 8
Bit 7
DACxCON
DACEN
—
DACSIDL
AMPON
—
—
—
FORM
—
DACxSTAT
LOEN
—
LMVOEN
—
—
LITYPE
LFULL
LEMPTY
ROEN
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit1
Bit 0
RITYPE
RFULL
REMPTY
DACFDIV<6:0>
—
RMVOEN
—
—
All Resets
0000
0000
DACxDFLT
DACDFLT<15:0>
DACxRDAT
DACRDAT<15:0>
0000
DACxLDAT
DACLDAT<15:0>
0000
Legend:
x = unknown value on Reset, — = unimplemented, read as ‘0’. Reset values are shown in hexadecimal.
0000
dsPIC33F Family Reference Manual
DS70211B-page 33-18
33.10
© 2009 Microchip Technology Inc.
Section 33. Audio Digital-to-Analog Converter (DAC)
33.11
RELATED APPLICATION NOTES
This section lists application notes that are related to this section of the manual. These
application notes may not be written specifically for the dsPIC33F product family, but the
concepts are pertinent and could be used with modification and possible limitations. The current
application notes related to the Audio Digital-to-Analog Converter (DAC) module are:
Title
Application Note #
No related application notes are available at this time.
Note:
N/A
Please visit the Microchip web site (www.microchip.com) for additional Application
Notes and code examples for the dsPIC33F family of devices.
33
Audio
Digital-to-Analog
Converter (DAC)
© 2009 Microchip Technology Inc.
DS70211B-page 33-19
dsPIC33F Family Reference Manual
33.12
REVISION HISTORY
Revision A (October 2007)
This is the initial released version of this document.
Revision B (September 2009)
This revision includes the following updates:
• Equations:
- Added the FVCO equation (see Equation 33-1) in 33.4.2 “Clock”.
• Figures:
- Updated the + and - signs and input signal names on both differential amps in
Figure 33-5.
• Notes:
- Added a note on the Audio DAC module usage in 33.2 “Key Features”.
• Sections:
- Added the DAC code example in 33.4.2 “Clock”.
- Added 33.11 “Related Application Notes”.
- Deleted the following description in 33.1 “Introduction”:
The positive and negative outputs are differential about a midpoint voltage of
approximately 1.65 volts with a voltage swing of approximately ±1 volt. The signals are
capable of driving a 1 kΩ load.
- Deleted the “Signal-to-noise ratio: 90 dB” in 33.2 “Key Features”.
- Deleted the following description in 33.4 “Module Operation”:
The differential outputs from the reconstruction filter are amplified by analog amplifiers
to provide the required 2V peak-to-peak voltage swing into a 1 kΩ load.
• Additional minor corrections such as language and formatting updates have been
incorporated throughout the document.
DS70211B-page 33-20
© 2009 Microchip Technology Inc.