AVR335: Digital Sound Recorder with AVR and Serial DataFlash

AVR335: Digital Sound Recorder with AVR® and
Serial DataFlash®
Features
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Digital Voice Recorder
8-bit Sound Recording
8 kHz Sampling Rate
Sound Frequency up to 4000 Hz
Maximum Recording Time 4 1/4 Minutes
Very Small Board Size
Only 550 Bytes of Code
Introduction
This application note describes how to
record, store and play back sound using
any AVR microcontroller with A/D conve rte r, the AT4 5DB1 61 DataFl as h
memory and a few extra components.
This application note shows in detail the
usage of the A/D Converter for sound
recording, the Serial Peripheral Interface
(SPI) for accessing the external
DataFlash memory and the Pulse Width
Modulation (PWM) for playback. Typical
applications that would require one or
more of these blocks are temperature
loggers, telephone answering machines,
or digital voice recorders.
The AT45DB161 DataFlash is a 2.7-volt
only, serial-interface Flash memory. Its
16M-bit of memory are organized as
4096 pages of 528 bytes each. In addition to its main memory, the DataFlash
contains two SRAM data buffers of 528
bytes each. The buffers allow a virtually
continuous data stream to be written to
the DataFlash.
The AT45DB161 uses an SPI serial
interface to sequentially access its data.
This interface facilitates hardware layout,
increases system reliability, minimizes
switching noise, and reduces package
size and active pin count. Typical applications are image storage, data storage
and digital voice storage. The DataFlash
operates at SPI clock frequencies up to
13 MHz with a typical active read current
consumption of 4 mA. It operates from a
single voltage power supply (from 2.7V
to 3.6V) for both the write and read
operations.
Its serial interface is compatible to the
Serial Peripheral Interface (SPI) Modes
0 and 3, thus it can easily be interfaced
to the AVR microcontroller.
8-bit
Microcontroller
Application
Note
In this application note the AVR
AT90S8535 is used to take analog samples from a microphone and convert
them to digital values. Its built-in SPI
controls data transfers to and from the
DataFlash. The PWM feature of the AVR
is used for playback. The code size is
very small (<550 bytes), the application
will therefore fit into the small
AT90S2333, a 28-pin device with 2K
Flash.
Theory of Operation
Before the analog speech signal can be
stored in the DataFlash it has to be converted into a digital signal. This is done
in multiple steps.
Figure 1. The Example Analog Signal
X(t)
0
t
Rev. 1456A–10/99
1
First, the analog signal (Figure 1) is converted into a time
discrete signal by taking periodic samples (Figure 2). The
time interval between two samples is called the “sampling
period” and its reciprocal the “sampling frequency”. According to the sampling theorem, the sampling frequency has to
be at least double the maximum signal frequency. Otherwise the periodic continuation of the signal in the frequency
domain would result in spectral overlap, called “aliasing”.
Such an aliased signal can not be uniquely recovered from
its samples.
A speech signal contains its major information below 3000
Hz. Therefore a low-pass filter can be used to band-limit
the signal.
For an ideal low-pass filter with a cut-off frequency of 3000
Hz the sampling frequency must be 6000 Hz. Depending
on the filter, the filter slope is more or less steep. Especially
for a first order filter like the RC-filter used in this application it is necessary to choose a much higher sampling
frequency. The upper limit is set by the features of the A/Dconverter.
Determining the digital values that represent the analog
samples taken at this sampling frequency is called “quantization”. The analog signal is quantized by assigning an
analog value to the nearest “allowed” digital value (Figure
3). The number of digital values is called “resolution” and is
always limited, e.g. to 256 values for an 8-bit digital signal
or 10 values in this example. Therefore quantization of analog signals always results in a loss of information. This
“quantization error” is inverse proportional to the resolution
of the digital signal. It is also inverse proportional to the signal’s “dynamic range”, the range between minimum and
maximum values (3 to 8 in this example). The A/D converter of the AT90S8535 microcontroller can be adjusted to
the dynamic range of the signal by setting AGND and
AREF to the minimum and maximum signal values.
On the other hand, the microphone amplifier can be
adjusted to cover the ADC’s dynamic range as presented
later.
Both methods reduce the quantization error. In addition,
the latter method also increases the signal-to-noise ratio
(SNR) and should therefore be preferred.
Figure 4 shows the digital values that represent the analog
signal. These are the values that are read as ADC conversion results.
In this application, the signal has a minimum and a maximum value which are never exceeded. The parts of the
signal below the minimum and above the maximum value
do not contain any information. They can be removed in
order to save memory.
This is done by downshifting the whole signal and discarding the part above the “max” value (Figure 5).
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AVR335
Figure 2. The Time Discrete Signal
X(t)
1 2 3 4 5 6 7 8 9
0
n
Figure 3. The Quantized Signal
X(t)
9
8
7
6
5
4
3
2
1
1 2 3 4 5 6 7 8 9
0
n
Figure 4. The Digital Signal
X(t)
9
8
7
6
5
4
3
2
1
1 2 3 4 5 6 7 8 9
0
n
Figure 5. The Bit-Reduced Digital Signal
X(t)
9
8
7
6
5
4
3
2
1
0
max
1 2 3 4 5 6 7 8 9
n
In this application the resulting signal has 8 bits. This signal
can now be stored in the DataFlash.
The DataFlash does not require a separate erase cycle
prior to programming. When using the "Buffer to Main
Memory Page Program with Built-In Erase" or "Main Memory Page Program Through Buffer" commands, the
AVR335
DataFlash will automatically erase the specified page
within the memory array before programming the actual
data. If systems require faster programming throughputs
(greater than 200K bps), then areas of the main memory
array can be pre-erased to reduce overall programming
times. An optional "Page Erase" command is provided to
erase a single page of memory while the optional "Block
Erase" command allows eight pages of memory to be
erased at one time. When pre-erasing portions of the main
memory array, the "Buffer to Main Memory Page Program
without Built-In Erase" command should be utilized to
achieve faster programming times.
The first method is the most code efficient, as no extra
erase cycles have to be implemented. This application
note, however, uses the block erase to illustrate how large
portions of the memory can be pre-erased if so desired.
Erasing the entire memory can take up to a few seconds.
After the memory has been erased, data can be recorded
until all pages are filled up.
For writing to the DataFlash, Buffer 1 is used. When this
buffer is filled up (with 528 samples) the buffer is written to
the main memory while the 529th conversion is done. Data
is recorded until the “Record” button is released or the
memory is full. If the entire memory is filled up, no new data
can be stored before the DataFlash is erased. If the memory is only partly filled and the “Record” button is pressed a
second time, the new data is appended directly to the existing data.
Playback of sound is always started at the beginning of the
DataFlash. It stops when either all recorded data is played
back or when the “Playback” button is released.
The DataFlash allows reading back data either directly
from a main memory page or by copying a page to one of
the two buffers and reading from the buffer. The direct
access method is not suitable for this application as two
addresses, one for page and one for byte position, and a
long initialization sequence have to be transferred to the
DataFlash for each single byte. This takes much longer
than one PWM cycle, which is 510 clock cycles for an 8-bit
PWM signal.
Therefore, one memory page is copied to one of the two
buffers. While data is read from this buffer the next memory
page is copied into the other buffer. When all data has
been read from the first buffer reading continues on the
other buffer, while the first one is reloaded.
Reading data from the DataFlash buffer is synchronized to
the PWM frequency.
Figure 6. Two Example PWM Cycles
PWM Counter
8
7
6
5
4
3
2
1
0
PWM Cycle Number
1 2 3 4 5 6 7 8 7 6 5 4 3 2 1 0 1 2 3 4 5 6 7 8 7 6 5 4 3 2 1 0
The digital value is played back by using pulse width modulation (PWM). In Figure 6, samples 2 and 3 of the example
signal are shown. One cycle of the PWM signal consists of
a counter counting up to the maximum value that can be
represented by the given resolution (8 in this example), and
counting down to zero again. The output is switched on
when the PWM counter matches the value of the digital signal value and is switched off when it falls below this value
again. Therefore the dark area represents the power of the
signal at that sample. Figure 7 shows the PWM output signal for the example signal.
The PWM frequency has to be at least twice the signal frequency. A PWM frequency at least four times higher is
recommended, depending on the output filter.
This can be achieved either by reducing signal frequency,
increasing system clock frequency or reducing signal
resolution.
Figure 7. The Filtered PWM Output Signal
X(t)
9
8
7
6
5
4
3
2
1
0
max
1 2 3 4 5 6 7 8 9
n
3
In this application the cut-off frequency of the output filter is
set to 4000 Hz, which is roughly one quarter of the PWM
frequency (15,686 Hz).
(which are very large in this example as only 8 digital values are used) and a missing amplification, the signal looks
almost like the analog input signal (Figure 1).
The system clock speed and the PWM resolution determines the PWM frequency.
Figure 8. The PWM Output Signal
With an 8 MHz system clock, the frequency for a 10-bit
PWM is 3922 Hz (8 MHz / 2 • 210 = 3922 Hz), 7843 Hz for
9-bit resolution, and 15,686 Hz for 8-bit resolution.
X(t)
9
8
7
6
5
4
3
2
1
Only the last value is high enough to serve as carrier frequency for the 4000 Hz signal. Therefore, the original 10-bit
digital sample is converted to 8 bits.
The output filter smoothens the output signal and removes
the high-frequency PWM carrier signal. The resulting output signal for the example signal now looks somehow like
the drawing in Figure 8. Except for the quantization errors
0
n
1 2 3 4 5 6 7 8 9
Microcontroller and Memory Circuit
ISP (SCK)
ISP (MOSI)
Vcc
ISP (MISO)
Figure 9. Microcontroller and Memory Circuit Diagram
Vcc
Vcc
Vcc
10K
1K
PB3
from microphone circuit
(Connector Pin 2)
RESET
RDY/BSY
WP
CS
SI
SO
SCK
PB0
PB1
PB2
PB4
MOSI
MISO
SCK
Vcc
OC1B
ADC0
AVR
AT90S8535
erase
PD0
to filter and amplifier circuit
(Connector Pin 3)
Vcc
Vcc
DataFlash
AT45DB161
GND
record
PD1
playback
100R
PD2
AGND
GND
GND
GND
AVcc
AREF
XTAL1
XTAL2
100nF
GND
GND
8MHz
22pF
22pF
GND
The user can control the sound system with three pushbuttons, called “erase”, “record” and “playback”. If the
pushbuttons are not pressed, the internal pull-up resistors
provide VCC at PD0 - PD2. Pushing a button pulls the input
line to GND.
reprogram the AVR, the pull-up resistor on the Chip Select
line (CS) prevents the DataFlash from going active. If the
ISP feature is not used, this resistor can be omitted.
As feedback for the user, an LED indicates the status of the
system.
The oscillator crystal with two 22 pF decoupling capacitors
generates the system clock.
The DataFlash is directly connected to the AVR microcontroller using the SPI bus. In case the ISP feature is used to
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AVR335
The analog voltage, AVCC, is connected to VCC by an RC
low-pass filter. The reference voltage is set to AVCC.
AVR335
Microphone and Speaker Circuit
Figure 10. Microphone and Speaker Circuit Diagram
R1
10K
Vcc
Vcc
R3
Vcc
U1A
5
3
1K
4
Vcc
10K
R4
3
C1
R9
2
2
1µF
1
4
+
1
R5
1
2
-
3
12K
11 LM 324
1K
4
R2
Microphone
GND
C8
4n7
GND
10K
Connector
GND
GND
GND
Vcc
C6
100nF
C2
C5
1µF
100nF
6 -
9
U1B
470R
R6
5K
5 +
C7
1nF
-
13
U1C
R7
1K8
LM 324
R10
15K
GND
The microphone amplifier is a simple inverting amplifier.
The gain is set with R1 and R9 (gain = R1 / R9). R4 is used
to power the microphone and C1 blocks any DC component to the amplifier. R2 and R3 set the offset. R5 and C8
form a simple first order low-pass filter. In addition R5 protects the amplifier from any damage if the output is shortcircuited.
The speaker circuit consists of a 5th-order, low-pass Chebychev filter and a unary-gain amplifier.
The filter is made up by two stagger-tuned, 2nd-order Chebychev filters (R6, R7, R8, C2, C7 and R7, R10, R11, C9,
C5) and a passive 1st-order filter (R11, C4). The cut-off frequencies of these three filters are slightly shifted against
each other (“staggered”) to limit passband ripple of the
whole filter circuit. The overall cut-off frequency is set to
4000 Hz, which is roughly one-quarter of the PWM frequency (15,686 Hz).
The unary-gain amplifier prevents the circuit from getting
feedback from the output.
C3 blocks any DC component to the speaker.
10 +
LM 324
R11
U1D
12 +
12K
C4
22nF
2n2
GND
C3
5
1µF
LM 324
C9
GND
-
14
8
7
R8
GND
4
3
2
1
Loudspeaker/
GND Headphones
Implementation
Setup
When the program is started the ports have to be set up.
This is done in the “setup” subroutine.
The SPI protocol defines one device as a master and the
other devices connected to this master as slaves. In this
application the AVR microcontroller functions as a master
and the DataFlash as a slave. As the AT90S8535 is the
only master in this application the SS pin can be used as
an I/O pin.
The SPI of the AT90S8535 is defined as an alternative
function of Port B (PB5 to PB7). In this application the control signals for the DataFlash are also set up on Port B
(PB0 to PB2 and PB4). The free pin (PB3) is used to control the status LED. For master setup, the signals Serial
Clock (SCK), Master Out/Slave In (MOSI), Chip Select
(CS), Write Protect (WP) and Reset (RST) are outputs,
whereas Master In/Slave Out (MISO) and Ready/Busy
(RDY/BSY) are inputs. With PB3 for the LED also defined
as an output the Data Direction Register for Port B is set up
as 0xBD.
Then the PortB is set to a defined status with all outputs
high and internal pull-up resistors on the inputs.
5
The A/D converter of the AT90S8535 is connected to
PortA. Therefore PortA is defined as a high-impedance
input.
Erase
PortD serves as an input for the pushbuttons and as an
output for the PWM signal. Here the PWM function of
Timer1 on the output pin PD4 is used.
Figure 12. Erase
In the end, interrupts are enabled. In this application two
interrupts (“ADC” and “Timer1 Overflow”) are used, which
are enabled and disabled directly in the subroutine when
they are required.
The Main Loop
The DataFlash can be optionally pre-erased.
Erase
Set block counter to zero
Set new-data flag
Enable SPI
In the main loop, the three pushbuttons are scanned. If one
of them is pressed, the LED is turns on to show that the
system is busy and the corresponding subroutine is called.
An extra loop is performed, until the button is released, as a
software debounce for the “Erase” and “Playback”
functions.
During the main loop, the LED is turned off to indicate that
the system is running idle.
Figure 11. The Main Loop
All blocks erased ?
YES
NO
Enable DataFlash
Disable SPI
Transmit
"block erase" opcode
Return
Start
Setup Ports
Transmit block address
Record
button
pressed
?
YES
Transmit don't cares
Record
NO
Disable DataFlash
Increment block counter
Erase
button
pressed
?
YES
Erase
Erase
button
released
?
NO
YES
NO
Block erase ready ?
Play back
button
pressed
?
NO
YES
Play back
Play back
button
released
?
NO
NO
YES
YES
When the “erase” subroutine is called, a flag is set which
indicates that in the next recording cycle the new data can
be stored at the beginning of the DataFlash.
LED off
The SPI has to be set up for accessing the DataFlash. No
interrupts are used here. The data order for the DataFlash
is MSB first and the AT90S8535 is the master.
6
AVR335
AVR335
The DataFlash accepts either the SCK signal being low
when CS toggles from high to low (SPI Mode 0) or the SCK
signal being high when CS toggles from high to low (SPI
Mode 3) with a positive clock phase. In this application the
SPI is set up in Mode 3. In order to get the fastest data
transfer possible, the lowest clock division is chosen, running the SPI bus at 2 MHz if an oscillator crystal of 8 MHz is
used.
To perform a block erase, the CS line is driven low and the
opcode 0x50 is loaded into the DataFlash followed by two
reserved bits (zeros), the 9-bit block address, and 13 don’t
care bits. This sequence is transferred to the slave bytewise. After each byte, the SPI Status Register (SPSR) is
checked until the SPI Interrupt Flag indicates that the serial
transfer is complete. After the whole sequence is written,
erasing of the block is started when the CS line is driven
high. The Ready/Busy pin is driven low by the DataFlash
until the block is erased. Then the next block will be erased
in the same way as the current. This takes place until all
512 blocks are erased. An erased location reads 0xFF.
Record
The record subroutine consists of the setup of the A/D converter and an empty loop which is performed as long as the
“record” button is pressed. The ADC0 pin is used in this
application which requires the ADC Multiplexer Select Register (ADMUX) being set to zero. In the ADC Control and
Status Register (ADCSR) the ADC is enabled with a clock
division factor of 32, set to single conversion mode, interrupts enabled, and the interrupt flag is cleared. The A/D
conversion is also immediately started. The first conversion
takes longer than the following conversions (832 oscillator
cycles instead of 448). After this time, the ADC interrupt
occurs indicating that the conversion is finished and the
result can be read out of the ADC Data Register.
The analog signal from the microphone circuit is sampled
at 15,686 Hz. This is the same frequency as the output
(PWM) frequency.
To achieve a sampling frequency of 15,686 Hz, a sample
has to be taken every 510 cycles (15,686 Hz x 510 = 8
MHz). To get one A/D conversion result, each 510 clock
cycles the ADC is run in single conversion mode with an
ADC clock division by 32. A single conversion takes 14
ADC cycles. Therefore a conversion will be ready after
14 x 32 = 448 cycles.
When a conversion is finished an interrupt occurs. The
interrupt routine then performs a loop to fill in the missing
510 - 448 = 62 cycles, before a new A/D conversion is
started.
The 10-bit conversion result represents the value at the
A/D converter input pin 2 cycles after the conversion has
started. These 10 bits cover the range from AGND to
AREF, which is 0 to 5V in this application. The microphone
circuit output signal, however, is limited to the range of
2.3V to 3.5V. Therefore the 10-bit conversion result is subtracted by a value representing the minimum input voltage.
This is 0x1D5 for 2.3V. The part of the data representing
signal values above 3.5V is removed by cutting off the two
MSBs. This is done automatically when the conversion
result is handed over to the “write to flash” subroutine, as
its variable “flash_data” is defined as type “char” (8-bit).
The final 8-bit data has then to be written to the DataFlash
before the next A/D conversion interrupt occurs.
Figure 13. Record
record
Initialize SPI
Initialize and start ADC
Record
button
pressed
?
NO
YES
Return
ADC ready ?
NO
YES
Loop for 62 cycles
Start A/D conversion
Read data from ADC
Convert data to 8 bit
Write to flash
7
Write to DataFlash
Writing data to the DataFlash is done by writing first to a
buffer and when this buffer is full writing it’s contents to one
page of the main memory.
Figure 14. Write to DataFlash
In the subroutine “write_to_flash” the variable “j” represents
the byte number in the buffer and the variable “k” the page
number the buffer will be written to. If the new-data flag
indicates that the DataFlash is empty, both counters are set
to zero.
write to flash
New-data flag set ?
NO
If the memory already contains some data, the variables
indicate the next free location in memory, which ensures
that new data is directly appended to the memory contents.
YES
Set page counter and
buffer counter to zero
In order to preserve the contents of these variables across
two function calls, they are declared as static variables.
Clear new-data flag
To write data to the buffer, the CS line is driven low and the
opcode 0x84 is loaded into the DataFlash. This is followed
by 14 don’t care bits and the 10-bit address for the position
within the buffer. Then the 8-bit data is entered.
YES
This sequence is transferred to the slave bytewise. After
each byte the SPI Status Register (SPSR) is checked until
the SPI Interrupt Flag indicates that the serial transfer is
complete. After the whole sequence is written the CS line is
driven high.
DataFlash busy ?
NO
Enable DataFlash
Disable DataFlash
If the buffer is full and there are empty pages left, the buffer
is copied to the next page of the DataFlash. As the memory
has been erased earlier, data can be written without additional erasing.
Buffer full ?
If the memory is filled, a loop is executed until the “record”
button is released. Any data recorded while the memory is
full will be lost.
Transmit
"buffer write" opcode,
buffer address and data
NO
YES
Set buffer counter to zero
Memory full ?
YES
NO
Enable DataFlash
LED off
Transmit
"buffer to page" opcode,
page address and
don't cares
Disable DataFlash
Record
button
released
?
YES
Increment page counter
Return
8
AVR335
NO
AVR335
Playback
In the “playback” subroutine, the contents of the DataFlash
are read out and modulated as an 8-bit PWM running at
15,686 Hz. To achieve higher speed, data is not read out
directly from the main memory but alternately transferred to
one of the two buffers and then read from the buffer. In the
meantime the next memory page is copied into the other
buffer. For the PWM, the 16-bit Timer/Counter1 is used
with the PWM output on OC1B. This is defined in the
Timer/Counter Control Registers A and B
(TCCRA/TCCRB). For running the PWM at the highest
possible frequency, the PWM clock divider is set to 1.
When the set-up is done, the first page is copied into Buffer
1 by driving the CS line low and transferring the appropriate
commands to the DataFlash. The page-to-buffer transfer is
started when the CS line is driven high again. When the
Ready/Busy pin is driven high by the DataFlash, Buffer 1
contains valid data. Then the next page transfer to Buffer 2
is started. As both buffers are independent from each
other, data can already be read from Buffer 1 while the
DataFlash is still busy copying data from the second page
to Buffer 2.
For reading a byte from a buffer, a dummy value has to be
written to the DataFlash. A write action of the master to an
SPI slave causes their SPI Data Register (SPDR) to be
interchanged. After writing a dummy byte to the DataFlash,
the SPDR of the AVR microcontroller contains the output
data from the DataFlash.
Figure 15. Playback
Playback
Set page counter to zero
Initialize PWM
Initialize SPI
next page to next buffer
next page
to next buffer
ready
?
NO
YES
End of memory
reached
?
YES
NO
button
for playback
pressed
?
YES
NO
Stop PWM
Stop SPI
Increment page counter
Return
next page to next buffer
active buffer to speaker
Toggle active buffer
When the PWM counter contains the value “0”, a Timer1
overflow interrupt occurs. This interrupt is used to synchronize data output from the DataFlash to the PWM frequency.
When a value from the buffer has been shifted to the AVR
microcontroller, a loop is performed until the Timer1 overflow interrupt occurs. Then the data is written to the
Timer/Counter1 Output Compare Register B (OCR1B),
being automatically latched to the PWM output when the
PWM counter contains its maximum value (255 for 8-bit
PWM).
9
After the last value of the buffer is read, the active buffer is
toggled.
Figure 17. Active Buffer to Speaker
active buffer to speaker
If the entire memory has been played back, all interrupts
are disabled and the Timer/Counter1 is stopped.
Set buffer counter to zero
Figure 16. Next Page to Next Buffer
Enable DataFlash
next page to next buffer
Transmit
"buffer read" opcode,
start buffer address
and don't cares
YES
DataFlash
busy?
NO
complete buffer
read
?
YES
Enable DataFlash
NO
Transmit
"page to buffer" opcode,
page number and
don't cares
Enable DataFlash
Send dummy value
to DataFlash
Return
Disable DataFlash
DataFlash
busy
?
Return
YES
Copy data from
SPI data register to
PWM data register
Increment buffer counter
10
AVR335
NO
AVR335
Using the STK200 Development Board
Modification and Optimization
The application described in this note can be tested and
modified using the STK200 Development Board. In this
case some points have to be noticed.
The microphone output signal may vary depending on the
type of microphone used. To achieve best results it is
important to choose the microphone amplifier gain that
delivers a maximum output signal closest to AREF.
Chip Socket
Data is written into the DataFlash almost as it is read from
the A/D converter. Compressing this data might be possible and useful if a longer recording time or a stereo signal
is required.
This application uses the A/D converter. Therefore the
microcontroller has to be placed in the socket labelled “A/D
parts” and the microphone amplifier output connected to
the header connectors labelled “Analog”.
Jumpers
According to the set-up in the “setup_all” subroutine all
jumpers on pins used for other purposes than pushbuttons
or the LED have to be removed. For the described application these are on Port B the jumpers 0 to 2 and 4 to 7 and
on Port D jumper 4.
SPI Resistors
In order to avoid interference between the on-board SPI
and devices connected to the pin headers labelled “Port B”,
10 kΩ resistors are inserted between the chip socket and
the Port B headers PB 5 to PB 7. If the DataFlash is going
to be connected to these pin headers, the resistors have to
be bypassed by soldering a bridge across their connectors
on the reverse side of the STK200.
Using the On-board SPI
Short circuiting the resistors between the chip socket and
the Port B header connectors may cause some problems if
using the on-board SPI for program download and verification, when a device is connected to the Port B header
connectors. If problems occur it will help either to disconnect the device during program download and verification,
or to solder a 10 kΩ resistor between PB4 and VCC according to Figure 9.
In this application two ways of implementing a status flag
are shown.
One way is to use a global variable (i.e. the “wait” variable
used in the “playback” subroutine). The other way is to use
an unused bit in a register. In the “erase” subroutine, the
ACIS1 bit of the Analog Comparator Control And Status
Register (ACSR) is used to indicate that new data has to be
stored next. As long as the analog comparator is not used
this does not have any negative effects on the program
performance, but frees one register from a blocking global
variable.
The sampling frequency of 15,686 Hz (respectively 510
clock cycles) is generated by an ADC interrupt and a delay
loop. This can be replaced by an independent timer
(Timer/Counter0 or Timer/Counter2), if they are not used
on other purposes.
References
1. Proakis, J.G. and Manolakis, D.G. (1992)
Digital Signal Processing: Principles, Algorithms, and
Applications
Second Edition
2. Datasheets:
Atmel AVR AT90S8535
Atmel AT45DB161 Serial DataFlash
11
Resources
Table 1. Peripheral Usage
Peripheral
Description
Interrupts
Timer 1
8-bit PWM
Timer 1 Overflow (PWM Counter at Zero)
3 I/O pins PORT B
SPI to Access DataFlash
4 I/O pins PORT B
DataFlash Control Lines
1 I/O pin PORT B
Status LED
1 I/O pin PORT A
ADC Input
3 I/O pins PORT D
Pushbuttons
1 I/O pin PORT D
PWM Output
A/D conversion ready
Bill of Materials
Table 2. Microcontroller and Memory Circuit
Component
Value
Description
R1
10 kΩ
Pull-up Resistor for DataFlash “Chip Select” Line
R2
1 kΩ
LED Resistor
R3
100Ω
Analog Voltage Filter Resistor
LED
Status Indicator
C1, C2
22 pF
Clock Signal Circuit Capacitors
C3
100 nF
Analog Voltage Filter Capacitor
Oscillator Crystal
8 MHz
Clock Signal Generation
DataFlash
AT45DB161
16M-bit Single Supply Nonvolatile Memory
AVR
AT90S8535
Enhanced RISC Flash Microcontroller
Table 3. Microphone and Speaker Circuit
Component
Value
Description
R1
10 kΩ
Feedback Resistor for Microphone Amplifier
R2
10 kΩ
Offset for Microphone Amplifier
R3
10 kΩ
Offset for Microphone Amplifier
R4
1 kΩ
Microphone Power Resistor
R5
12 kΩ
Microphone RC Filter Resistor
R6
5 kΩ
Chebychev Filter Resistor
R7
1 kΩ
Chebychev Filter Resistor
R8
470Ω
Chebychev Filter Resistor
R9
1 kΩ
Input Resistor for Microphone Amplifier
R10
15 kΩ
Chebychev Filter Resistor
12
AVR335
AVR335
Table 3. Microphone and Speaker Circuit (Continued)
Component
Value
Description
R11
12 kΩ
Earphones RC Filter Resistor
C1
1 µF
AC Coupling for Microphone
C2
1 µF
Chebychev Filter Capacitor
C3
1 µF
AC Coupling for Earphones
C4
22 nF
Earphones RC Filter Capacitor
C5
100 nF
Chebychev Filter Capacitor
C6
100 nF
De-coupling Capacitor
C7
1 nF
Chebychev Filter Capacitor
C8
4.7 nF
Earphones RC Filter Capacitor
C9
2.2 nF
Chebychev Filter Capacitor
U1
LM324
Quad Op-amp
2 standard jack sockets
3.5 mm
Microphone
Standard PC Microphone with 3.5 mm Connector
Earphones
Standard with 3.5 mm Connector
13
Sample C Code
/* Check the Atmel Web Site for latest version of the code.
/*
Erase all pages if desired.
Write data to buffer 1. If buffer is full, write buffer to page.
Read DataFlash alternating through buffer1 and buffer2 into the data register.
*/
#include “io8535.h”
#include <ina90.h>
#include “stdlib.h”
#include “dataflash.h”
// prototypes
void setup (void);
void erasing (void);
void recording (void);
void interrupt[ADC_vect] sample_ready (void);
void write_to_flash (unsigned char ad_data);
void playback (void);
void next_page_to_next_buffer (unsigned char active_buffer, unsigned int page_counter);
void interrupt[TIMER1_OVF1_vect] out_now(void);
void active_buffer_to_speaker (unsigned char active_buffer);
// global variables
volatile unsigned char wait = 0;
void setup(void)
{
DDRB = 0xBD;
// SCK, MISO, MOSI,
// SPI Port initialisation
CS, LED,
WP , RDYBSY, RST
// PB7, PB6,
PB5,
PB4, PB3, PB2 ,
PB1,
O
I
O
O
O
O
I
O
//
1
0
1
1
1
1
0
1
PORTB = 0xFF;
// all outputs high, inputs have pullups (LED is off)
DDRA = 0x00;
// define port A as an input
PORTA = 0x00;
DDRD = 0x10;
// define port D as an input (D4: output)
_SEI();
// enable interrupts
}
void erasing(void)
{
unsigned int block_counter = 0;
unsigned char temp = 0x80;
14
PB0
//
AVR335
AVR335
ACSR |= 0x02;
// set signal flag that new data has to be recorded next
// interrupt disabled, SPI port enabled, master mode, MSB first,
SPI mode 3, Fcl/4
SPCR = 0x5C;
while (block_counter < 512)
{
PORTB &= ~DF_CHIP_SELECT; // enable DataFlash
SPDR = BLOCK_ERASE;
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = (char)(block_counter>>3);
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = (char)(block_counter<<5);
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = 0x00;
// don’t cares
while (!(SPSR & temp));
// wait for data transfer to be completed
PORTB |= DF_CHIP_SELECT;
// disable DataFlash
block_counter++;
while(!(PINB & 0x02));
// wait until block is erased
}
SPCR = 0x00;
//disable SPI
}
void recording(void)
{
// interrupt disabled, SPI port enabled, master mode, MSB first, SPI mode 3, Fcl/4
SPCR = 0x5C;
ADMUX = 0x00;
// A/D converter input pin number = 0
ADCSR = 0xDD;
// single A/D conversion, fCK/32, conversion now started
while (!(PIND & 8));
// loop while button for recording (button 3) is pressed
ADCSR = 0x00;
// disable AD converter
SPCR = 0x00;
// disable SPI
}
void interrupt[ADC_vect] sample_ready(void)
{
unsigned char count = 0;
while (count < 6) count++;
// wait some cycles
ADCSR |= 0x40;
// start new A/D conversion
write_to_flash(ADC-0x1D5);
// read data, convert to 8 bit and store in flash
}
void write_to_flash(unsigned char flash_data)
15
{
static unsigned int buffer_counter;
static unsigned int page_counter;
unsigned char temp = 0x80;
if((ACSR & 0x02))
// if flag is set that new data has to be written
{
buffer_counter = 0;
page_counter = 0;
// reset the counter if new data has to be written
ACSR &= 0xFD;
// clear the signal flag
}
while(!(PINB & 0x02));
// check if flash is busy
PORTB &= ~DF_CHIP_SELECT;
// enable DataFlash
SPDR = BUFFER_1_WRITE;
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = 0x00;
// don’t cares
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = (char)(buffer_counter>>8);
// don’t cares plus first two bits of buffer address
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = (char)buffer_counter;
// buffer address (max. 2^8 = 256 pages)
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = flash_data;
// write data into SPI Data Register
while (!(SPSR & temp));
// wait for data transfer to be completed
PORTB |= DF_CHIP_SELECT;
// disable DataFlash
buffer_counter++;
if (buffer_counter > 528)
// if buffer full write buffer into memory page
{
buffer_counter = 0;
if (page_counter < 4096)
// if memory is not full
{
PORTB &= ~DF_CHIP_SELECT;
// enable DataFlash
SPDR = B1_TO_MM_PAGE_PROG_WITHOUT_ERASE; // write data from buffer1 to page
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = (char)(page_counter>>6);
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = (char)(page_counter<<2);
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = 0x00;
// don’t cares
while (!(SPSR & temp));
// wait for data transfer to be completed
PORTB |= DF_CHIP_SELECT;
// disable DataFlash
page_counter++;
16
AVR335
AVR335
}
else
{
PORTB |= 0x08;
// turn LED off
while (!(PIND & 8));
// wait until button for recording (button 3) is released
}
}
}
void playback(void)
{
unsigned int page_counter = 0;
unsigned int buffer_counter = 0;
unsigned char active_buffer = 1;
// active buffer = buffer1
unsigned char temp = 0x80;
TCCR1A = 0x21;
// 8 bit PWM, using COM1B
TCNT1 = 0x00;
// set counter1 to zero
TIFR = 0x04;
// clear counter1 overflow flag
TIMSK = 0x04;
// enable counter1 overflow interrupt
TCCR1B = 0x01;
// counter1 clock prescale = 1
OCR1B = 0x00;
// set output compare register B to zero
// interrupt disabled, SPI port enabled, master mode, MSB first,
SPI mode 3, Fcl/4
SPCR = 0x5C;
next_page_to_next_buffer (active_buffer, page_counter);
// read page0 to buffer1
while (!(PINB & 0x02));
// wait until page0 to buffer1 transaction is finished
while ((page_counter < 4095)&(!(PIND & 2)))
// while button for playback (button 1) is pressed
{
page_counter++;
// now take next page
next_page_to_next_buffer (active_buffer, page_counter);
active_buffer_to_speaker (active_buffer);
if (active_buffer == 1)
// if buffer1 is the active buffer
{
active_buffer++;
// set buffer2 as active buffer
}
else
// else
{
active_buffer--;
// set buffer1 as active buffer
}
}
TIMSK = 0x00;
// disable all interrupts
TCCR1B = 0x00;
// stop counter1
SPCR = 0x00;
// disable SPI
17
}
void next_page_to_next_buffer (unsigned char active_buffer, unsigned int page_counter)
{
unsigned char temp = 0x80;
while(!(PINB & 0x02));
// wait until flash is not busy
PORTB &= ~DF_CHIP_SELECT;
// enable DataFlash
if (active_buffer == 1)
// if buffer1 is the active buffer
{
SPDR = MM_PAGE_TO_B2_XFER;
// transfer next page to buffer2
}
else
// else
{
SPDR = MM_PAGE_TO_B1_XFER;
// transfer next page to buffer1
}
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = (char)(page_counter >> 6);
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = (char)(page_counter << 2);
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = 0x00;
// write don’t care byte
while (!(SPSR & temp));
// wait for data transfer to be completed
PORTB |= DF_CHIP_SELECT;
// disable DataFlash and start transaction
}
void interrupt[TIMER1_OVF1_vect] out_now(void)
{
wait = 0;
// an interrupt has occured
}
void active_buffer_to_speaker (unsigned char active_buffer)
{
// until active buffer not empty read active buffer to speaker
unsigned int buffer_counter = 0;
unsigned char temp = 0x80;
PORTB &= ~DF_CHIP_SELECT;
// enable DataFlash
if (active_buffer == 1)
// if buffer1 is the active buffer
{
SPDR = BUFFER_1_READ;
// read from buffer1
}
else
18
// else
AVR335
AVR335
{
SPDR = BUFFER_2_READ;
// read from buffer2
}
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = 0x00;
// write don’t care byte
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = 0x00;
// write don’t care byte
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = 0x00;
// start at buffer address 0
while (!(SPSR & temp));
// wait for data transfer to be completed
SPDR = 0x00;
// write don’t care byte
while (!(SPSR & temp));
// wait for data transfer to be completed
while (buffer_counter < 528)
{
SPDR = 0xFF;
// write dummy value to start register shift
while (!(SPSR & temp));
// wait for data transfer to be completed
while(wait);
// wait for timer1 overflow interrupt
OCR1B = SPDR;
// play data from shift register
wait = 1;
// clear the signal flag
buffer_counter++;
}
PORTB |= DF_CHIP_SELECT;
// disable DataFlash
}
void main(void)
{
setup();
for(;;)
{
if (!(PIND & 8))
// if button for recording (button 3) is pressed
{
PORTB &= 0xF7;
// turn LED on
recording();
}
if (!(PIND & 4))
// if button for erasing (button 2) is pressed
{
PORTB &= 0xF7;
// turn LED on
erasing();
while (!(PIND & 4));
// wait until button for erasing (button 2) is released
}
if (!(PIND & 2))
// if button for playback (button 1) is pressed
{
PORTB &= 0xF7;
// turn LED on
playback();
while (!(PIND & 2));
// wait until button for playback (button 1) is released
}
PORTB |= 0x08;
// turn LED off while running idle
19
}
}
DataFlash.h
// changed on 19.04.1999
// for use with the 8535
#include “ina90.h”
#pragma language=extended
// DataFlash reset port pin (PB 0)
#define DF_RESET 0x01
// DataFlash ready/busy status port pin (PB 1)
#define DF_RDY_BUSY 0x02
// DataFlash boot sector write protection (PB 2)
#define DF_WRITE_PROTECT 0x04
// DataFlash chip select port pin (PB 4)
#define DF_CHIP_SELECT 0x10
// buffer 1
#define BUFFER_1 0x00
// buffer 2
#define BUFFER_2 0x01
// defines for all opcodes
// buffer 1 write
#define BUFFER_1_WRITE 0x84
// buffer 2 write
#define BUFFER_2_WRITE 0x87
// buffer 1 read
#define BUFFER_1_READ 0x54
// buffer 2 read
#define BUFFER_2_READ 0x56
// buffer 1 to main memory page program with built-in erase
#define B1_TO_MM_PAGE_PROG_WITH_ERASE 0x83
// buffer 2 to main memory page program with built-in erase
#define B2_TO_MM_PAGE_PROG_WITH_ERASE 0x86
20
AVR335
AVR335
// buffer 1 to main memory page program without built-in erase
#define B1_TO_MM_PAGE_PROG_WITHOUT_ERASE 0x88
// buffer 2 to main memory page program without built-in erase
#define B2_TO_MM_PAGE_PROG_WITHOUT_ERASE 0x89
// main memory page program through buffer 1
#define MM_PAGE_PROG_THROUGH_B1 0x82
// main memory page program through buffer 2
#define MM_PAGE_PROG_THROUGH_B2 0x85
// auto page rewrite through buffer 1
#define AUTO_PAGE_REWRITE_THROUGH_B1 0x58
// auto page rewrite through buffer 2
#define AUTO_PAGE_REWRITE_THROUGH_B2 0x59
// main memory page compare to buffer 1
#define MM_PAGE_TO_B1_COMP 0x60
// main memory page compare to buffer 2
#define MM_PAGE_TO_B2_COMP 0x61
// main memory page to buffer 1 transfer
#define MM_PAGE_TO_B1_XFER 0x53
// main memory page to buffer 2 transfer
#define MM_PAGE_TO_B2_XFER 0x55
// DataFlash status register for reading density, compare status,
// and ready/busy status
#define STATUS_REGISTER 0x57
// main memory page read
#define MAIN_MEMORY_PAGE_READ 0x52
// erase a 528 byte page
#define PAGE_ERASE 0x81
// erase 512 pages
#define BLOCK_ERASE 0x50
#define TRUE
0xff
#define FALSE
0x00
21
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© Atmel Corporation 1999.
Atmel Corporation makes no warranty for the use of its products, other than those expressly contained in the Company’s standard warranty which is detailed in Atmel’s Terms and Conditions located on the Company’s web site. The Company assumes no responsibility for
any errors which may appear in this document, reserves the right to change devices or specifications detailed herein at any time without
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are registered trademarks and trademarks of Atmel Corporation.
Terms and product names in this document may be trademarks of others.
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