Tutorial.SPIEEPROM History

Hide minor edits - Show changes to output

October 07, 2006, at 06:30 PM by Heather Dewey-Hagborg -
Changed lines 16-17 from:
* Master In Slave Out (MISO) - The Master line for sending data to the peripherals,
* Master Out Slave In (MOSI) - The Slave line for sending data to the master,
to:
* Master In Slave Out (MISO) - The Slave line for sending data to the master,
* Master Out Slave In (MOSI) - The Master line for sending data to the peripherals,
September 06, 2006, at 11:30 PM by David A. Mellis - adding note about internal eeprom on arduino
Changed lines 3-4 from:
In this tutorial you will learn how to interface with an AT25HP512 Atmel serial EEPROM using the Serial Peripheral Interface (SPI) protocol. EEPROM chips such as this are very useful for data storage, and the steps we will cover for implementing SPI communication can be modified for use with most other SPI devices.
to:
In this tutorial you will learn how to interface with an AT25HP512 Atmel serial EEPROM using the Serial Peripheral Interface (SPI) protocol. EEPROM chips such as this are very useful for data storage, and the steps we will cover for implementing SPI communication can be modified for use with most other SPI devices. Note that the chip on the Arduino board contains an internal EEPROM, so follow this tutorial only if you need more space than it provides.
September 06, 2006, at 10:38 PM by Heather Dewey-Hagborg -
Changed lines 7-10 from:
# AT25HP512 Serial EEPROM chip (or similar)
# Hookup wire
# Arduino Microcontroller Module
to:
* AT25HP512 Serial EEPROM chip (or similar)
* Hookup wire
* Arduino Microcontroller Module
September 05, 2006, at 07:57 PM by Heather Dewey-Hagborg -
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@]
to:
@]

''code and tutorial by Heather Dewey-Hagborg, photos by Thomas Dexter''
August 31, 2006, at 08:19 PM by Heather Dewey-Hagborg -
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Connect EEPROM pin 1 to Arduino pin 10 (Slave Select), EEPROM pin 2 to Arduino pin 12 (Master In Slave Out), EEPROM pin 5 to Arduino pin 11 (Master Out Slave In), and EEPROM pin 6 to Arduino pin 13 (Serial Clock).
to:
Connect EEPROM pin 1 to Arduino pin 10 (Slave Select - SS), EEPROM pin 2 to Arduino pin 12 (Master In Slave Out - MISO), EEPROM pin 5 to Arduino pin 11 (Master Out Slave In - MOSI), and EEPROM pin 6 to Arduino pin 13 (Serial Clock - SCK).
August 31, 2006, at 08:17 PM by Heather Dewey-Hagborg -
Changed lines 68-69 from:
to:
''+5v wires are red, GND wires are black''
Changed lines 73-74 from:
to:
''SS wire is white, MISO wire is yellow, MOSI wire is blue, SCK wire is green''
August 31, 2006, at 08:13 PM by Heather Dewey-Hagborg -
Changed lines 67-68 from:
PICTURE of pwr wires
to:
Attach:eeprom_pwr.jpg
Changed lines 71-72 from:
PICTURE of SPI wires
to:
Attach:eeprom_signal.jpg
August 30, 2006, at 06:08 PM by Heather Dewey-Hagborg -
Changed lines 2-3 from:
(IN PROGRESS)
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August 30, 2006, at 06:05 PM by Heather Dewey-Hagborg -
Changed lines 180-182 from:

This function simply fills our data array with numbers 0 - 127 for each index in the array. This function could easily be changed to fill the array with data relevant to your application:
to:
The fill_buffer function simply fills our data array with numbers 0 - 127 for each index in the array. This function could easily be changed to fill the array with data relevant to your application:
Changed lines 191-192 from:
This function loads the output data into the data transmission register, thus starting the SPI transmission. It polls a bit to the SPI Status register (SPSR) to detect when the transmission is complete using a bit mask, SPIF. An explanation of bit masks can be found [[http://www.arduino.cc/en/Tutorial/BitMask | here]]. It then returns any data that has been shifted in to the data register by the EEPROM:
to:
The spi_transfer function loads the output data into the data transmission register, thus starting the SPI transmission. It polls a bit to the SPI Status register (SPSR) to detect when the transmission is complete using a bit mask, SPIF. An explanation of bit masks can be found [[http://www.arduino.cc/en/Tutorial/BitMask | here]]. It then returns any data that has been shifted in to the data register by the EEPROM:
Changed lines 203-204 from:
This function allows us to read data back out of the EEPROM. First we set the SLAVESELECT line low to enable the device. Then we transmit a READ instruction, followed by the 16-bit address we wish to read from, Most Significant Bit first. Next we send a dummy byte to the EEPROM for the purpose of shifting the data out. Finally we pull the SLAVESELECT line high again to release the device after reading one byte, and return the data. If we wanted to read multiple bytes at a time we could hold the SLAVESELECT line low while we repeated the [@data = spi_transfer(0xFF);@] up to 128 times for a full page of data:
to:
The read_eeprom function allows us to read data back out of the EEPROM. First we set the SLAVESELECT line low to enable the device. Then we transmit a READ instruction, followed by the 16-bit address we wish to read from, Most Significant Bit first. Next we send a dummy byte to the EEPROM for the purpose of shifting the data out. Finally we pull the SLAVESELECT line high again to release the device after reading one byte, and return the data. If we wanted to read multiple bytes at a time we could hold the SLAVESELECT line low while we repeated the [@data = spi_transfer(0xFF);@] up to 128 times for a full page of data:
August 30, 2006, at 06:05 PM by Heather Dewey-Hagborg -
Added lines 78-81:
The first step is setting up our pre-processor directives. Pre-processor directives are processed before the actual compilation begins. They start with a "#" and do not end with semi-colons.

We define the pins we will be using for our SPI connection, DATAOUT, DATAIN, SPICLOCK and SLAVESELECT. Then we define our opcodes for the EEPROM. Opcodes are control commands:
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Here we set up our pre-processor directives. Pre-processor directives are processed before the actual compilation begins. They start with a "#" and do not end with semi-colons.

First we define the pins we will be using for our SPI connection, DATAOUT, DATAIN, SPICLOCK and SLAVESELECT. Then we define our opcodes for the EEPROM. Opcodes are control commands.
to:
Here we allocate the global variables we will be using later in the program. Note [@char buffer [128];@]. this is a 128 byte array we will be using to store the data for the EEPROM write:
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Here we allocate the global variables we will be using later in the program. Note [@char buffer [128];@]. this is a 128 byte array we will be using to store the data for the EEPROM write.
to:
First we initialize our serial connection, set our input and output pin modes and set the SLAVESELECT line high to start. This deselects the device and avoids any false transmission messages due to line noise:
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First we initialize our serial connection, set our input and output pin modes and set the SLAVESELECT line high to start. This deselects the device and avoids any false transmission messages due to line noise.
to:
Now we set the SPI Control register (SPCR) to the binary value 01010000. In the control register each bit sets a different functionality. The eighth bit disables the SPI interrupt, the seventh bit enables the SPI, the sixth bit chooses transmission with the most significant bit going first, the fifth bit puts the Arduino in Master mode, the fourth bit sets the data clock idle when it is low, the third bit sets the SPI to sample data on the rising edge of the data clock, and the second and first bits set the speed of the SPI to system speed / 4 (the fastest).
After setting our control register up we read the SPI status register (SPSR) and data register (SPDR) in to the junk clr variable to clear out any spurious data from past runs:
Changed lines 131-133 from:
Now we set the SPI Control register (SPCR) to the binary value 01010000. In the control register each bit sets a different functionality. The eighth bit disables the SPI interrupt, the seventh bit enables the SPI, the sixth bit chooses transmission with the most significant bit going first, the fifth bit puts the Arduino in Master mode, the fourth bit sets the data clock idle when it is low, the third bit sets the SPI to sample data on the rising edge of the data clock, and the second and first bits set the speed of the SPI to system speed / 4 (the fastest).
After setting our control register up we read the SPI status register (SPSR) and data register (SPDR) in to the junk clr variabl to clear out any spurious data from past runs.
to:
Here we fill our data array with numbers and send a write enable instruction to the EEPROM. The EEPROM MUST be write enabled before every write instruction. To send the instruction we pull the SLAVESELECT line low, enabling the device, and then send the instruction using the spi_transfer function. Note that we use the WREN opcode we defined at the beginning of the program. Finally we pull the SLAVESELECT line high again to release it:
Changed lines 141-142 from:
Here we fill our data array with numbers and send a write enable instruction to the EEPROM. The EEPROM MUST be write enabled before every write instruction. To send the instruction we pull the SLAVESELECT line low, enabling the device, and then send the instruction using the spi_transfer function. Note that we use the WREN opcode we defined at the beginning of the program. Finally we pull the SLAVESELECT line high again to release it.
to:
Now we pull the SLAVESELECT line low to select the device again after a brief delay. We send a WRITE instruction to tell the EEPROM we will be sending data to record into memory. We send the 16 bit address to begin writing at in two bytes, Most Significant Bit first. Next we send our 128 bytes of data from our buffer array, one byte after another without pause. Finally we set the SLAVESELECT pin high to release the device and pause to allow the EEPROM to write the data:
Changed lines 159-160 from:
Now we pull the SLAVESELECT line low to select the device again after a brief delay. We send a WRITE instruction to tell the EEPROM we will be sending data to record into memory. We send the 16 bit address to begin writing at in two bytes, Most Significant Bit first. Next we send our 128 bytes of data from our buffer array, one byte after another without pause. Finally we set the SLAVESELECT pin high to release the device and pause to allow the EEPROM to write the data.
to:
We end the setup function by sending the word "hi" plus a line feed out the built in serial port for debugging purposes. This way if our data comes out looking funny later on we can tell it isn't just the serial port acting up:
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We end the setup function by sending the word "hi" plus a line feed out the built in serial port for debugging purposes. This way if our data comes out looking funny later on we can tell it isn't just the serial port acting up.
to:

In our main loop we just read one byte at a time from the EEPROM and print it out the serial port. We add a line feed and a pause for readability. Each time through the loop we increment the eeprom address to read. When the address increments to 128 we turn it back to 0 because we have only filled 128 addresses in the EEPROM with data:
Changed lines 181-182 from:
In our main loop we just read one byte at a time from the EEPROM and print it out the serial port. We add a line feed and a pause for readability. Each time through the loop we increment the eeprom address to read. When the address increments to 128 we turn it back to 0 because we have only filled 128 addresses in the EEPROM with data.
to:
This function simply fills our data array with numbers 0 - 127 for each index in the array. This function could easily be changed to fill the array with data relevant to your application:
Changed lines 192-193 from:
This function simply fills our data array with numbers 0 - 127 for each index in the array. This function could easily be changed to fill the array with data relevant to your application.
to:
This function loads the output data into the data transmission register, thus starting the SPI transmission. It polls a bit to the SPI Status register (SPSR) to detect when the transmission is complete using a bit mask, SPIF. An explanation of bit masks can be found [[http://www.arduino.cc/en/Tutorial/BitMask | here]]. It then returns any data that has been shifted in to the data register by the EEPROM:
Changed lines 204-205 from:
This function loads the output data into the data transmission register, thus starting the SPI transmission. It polls a bit to the SPI Status register (SPSR) to detect when the transmission is complete using a bit mask, SPIF. An explanation of bit masks can be found [[http://www.arduino.cc/en/Tutorial/BitMask | here]]. It then returns any data that has been shifted in to the data register by the EEPROM.
to:
This function allows us to read data back out of the EEPROM. First we set the SLAVESELECT line low to enable the device. Then we transmit a READ instruction, followed by the 16-bit address we wish to read from, Most Significant Bit first. Next we send a dummy byte to the EEPROM for the purpose of shifting the data out. Finally we pull the SLAVESELECT line high again to release the device after reading one byte, and return the data. If we wanted to read multiple bytes at a time we could hold the SLAVESELECT line low while we repeated the [@data = spi_transfer(0xFF);@] up to 128 times for a full page of data:
Changed lines 220-222 from:
This function allows us to read data back out of the EEPROM. First we set the SLAVESELECT line low to enable the device. Then we transmit a READ instruction, followed by the 16-bit address we wish to read from, Most Significant Bit first. Next we send a dummy byte to the EEPROM for the purpose of shifting the data out. Finally we pull the SLAVESELECT line high again to release the device after reading one byte, and return the data. If we wanted to read multiple bytes at a time we could hold the SLAVESELECT line low while we repeated the [@data = spi_transfer(0xFF);@] up to 128 times for a full page of data.

to:
August 30, 2006, at 06:01 PM by Heather Dewey-Hagborg -
Changed line 107 from:
void fill_buffer()
to:
void setup()
Deleted lines 108-132:
for (int I=0;I<128;I++)
{
buffer[I]=I;
}
} @]

This function simply fills our data array with numbers 0 - 127 for each index in the array. This function could easily be changed to fill the array with data relevant to your application.

[@
char spi_transfer(volatile char data)
{
SPDR = data; // Start the transmission
while (!(SPSR & (1<<SPIF))) // Wait for the end of the transmission
{
};
return SPDR; // return the received byte
}@]

This function loads the output data into the data transmission register, thus starting the SPI transmission. It polls a bit to the SPI Status register (SPSR) to detect when the transmission is complete using a bit mask, SPIF. An explanation of bit masks can be found [[http://www.arduino.cc/en/Tutorial/BitMask | here]]. It then returns any data that has been shifted in to the data register by the EEPROM.

The following setup function is long so we will take it in parts.

[@
void setup()
{
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delay(1000);@]
to:
delay(1000);
}@]
Changed line 169 from:
byte read_eeprom(int EEPROM_address)
to:
void loop()
Changed lines 171-179 from:
//READ EEPROM
int data;
digitalWrite(SLAVESELECT,LOW);
spi_transfer(READ); //transmit read opcode
spi_transfer((char)(EEPROM_address>>8)); //send MSByte address first
spi_transfer((char)(EEPROM_address)); //send LSByte address
data = spi_transfer(0xFF); //get data byte
digitalWrite(SLAVESELECT,HIGH); //release chip, signal end transfer
return data;
to:
eeprom_output_data = read_eeprom(address);
Serial.print(eeprom_output_data,DEC);
Serial.print('\n',BYTE);
address++;
delay(500); //pause for readability
Changed lines 178-179 from:
This function allows us to read data back out of the EEPROM. First we set the SLAVESELECT line low to enable the device. Then we transmit a READ instruction, followed by the 16-bit address we wish to read from, Most Significant Bit first. Next we send a dummy byte to the EEPROM for the purpose of shifting the data out. Finally we pull the SLAVESELECT line high again to release the device after reading one byte, and return the data. If we wanted to read multiple bytes at a time we could hold the SLAVESELECT line low while we repeated the [@data = spi_transfer(0xFF);@] up to 128 times for a full page of data.
to:
In our main loop we just read one byte at a time from the EEPROM and print it out the serial port. We add a line feed and a pause for readability. Each time through the loop we increment the eeprom address to read. When the address increments to 128 we turn it back to 0 because we have only filled 128 addresses in the EEPROM with data.
Changed line 181 from:
void loop()
to:
void fill_buffer()
Changed lines 183-187 from:
eeprom_output_data = read_eeprom(address);
Serial.print(eeprom_output_data,DEC);
Serial.print('\n',BYTE);
address++;
delay(500); //pause for readability
to:
for (int I=0;I<128;I++)
{
buffer[I]=I;
}
Changed lines 189-193 from:
Finally we get to our main loop, the simplest function in the program! Here we just read one byte at a time from the EEPROM and print it out the serial port. We add a line feed and a pause for readability. Each time through the loop we increment the eeprom address to read. When the address increments to 128 we turn it back to 0 because we have only filled 128 addresses in the EEPROM with data.


For easy copy and pasting the full program text of this tutorial is below:
to:
This function simply fills our data array with numbers 0 - 127 for each index in the array. This function could easily be changed to fill the array with data relevant to your application.
Changed lines 192-212 from:
#define DATAOUT 11//MOSI
#define DATAIN 12//MISO
#define SPICLOCK 13//sck
#define SLAVESELECT 10//ss

//opcodes
#define WREN 6
#define WRDI 4
#define RDSR 5
#define WRSR 1
#define READ 3
#define WRITE 2

byte eeprom_output_data;
byte eeprom_input_data=0;
byte clr;
int address=0;
//data buffer
char buffer [128];

void fill_buffer()
to:
char spi_transfer(volatile char data)
Changed lines 194-195 from:
for (int I=0;I<128;I++)
to:
SPDR = data; // Start the transmission
while (!(SPSR & (1<<SPIF))) // Wait for the end of the transmission
Deleted lines 196-204:
buffer[I]=I;
}
}

char spi_transfer(volatile char data)
{
SPDR = data; // Start the transmission
while (!(SPSR & (1<<SPIF))) // Wait the end of the transmission
{
Changed lines 199-201 from:
}

void setup()
to:
}@]

This function loads the output data into the data transmission register, thus starting the SPI transmission. It polls a bit to the SPI Status register (SPSR) to detect when the transmission is complete using a bit mask, SPIF. An explanation of bit masks can be found [[http://www.arduino.cc/en/Tutorial/BitMask | here]]. It then returns any data that has been shifted in to the data register by the EEPROM.

[@
byte read_eeprom(int EEPROM_address)
Changed lines 206-222 from:
Serial.begin(9600);

pinMode(DATAOUT, OUTPUT);
pinMode(DATAIN, INPUT);
pinMode(SPICLOCK,OUTPUT);
pinMode(SLAVESELECT,OUTPUT);
digitalWrite(SLAVESELECT,HIGH); //disable device
// SPCR = 01010000
//interrupt disabled,spi enabled,msb 1st,master,clk low when idle,
//sample on leading edge of clk,system clock/4 rate (fastest)
SPCR = (1<<SPE)|(1<<MSTR);
clr=SPSR;
clr=SPDR;
delay(10);
//fill buffer with data
fill_buffer();
//fill eeprom w/ buffer
to:
//READ EEPROM
int data;
Deleted lines 208-234:
spi_transfer(WREN); //write enable
digitalWrite(SLAVESELECT,HIGH);
delay(10);
digitalWrite(SLAVESELECT,LOW);
spi_transfer(WRITE); //write instruction
address=0;
spi_transfer((char)(address>>8)); //send MSByte address first
spi_transfer((char)(address)); //send LSByte address
//write 128 bytes
for (int I=0;I<128;I++)
{
spi_transfer(buffer[I]); //write data byte
}
digitalWrite(SLAVESELECT,HIGH); //release chip
//wait for eeprom to finish writing
delay(3000);
Serial.print('h',BYTE);
Serial.print('i',BYTE);
Serial.print('\n',BYTE);//debug
delay(1000);
}

byte read_eeprom(int EEPROM_address)
{
//READ EEPROM
int data;
digitalWrite(SLAVESELECT,LOW);
Changed lines 215-228 from:
}

void loop()
{
eeprom_output_data = read_eeprom(address);
Serial.print(eeprom_output_data,DEC);
Serial.print('\n',BYTE);
address++;
if (address == 128)
address = 0;
delay(500); //pause for readability
}
@]
to:
} @]

This function allows us to read data back out of the EEPROM. First we set the SLAVESELECT line low to enable the device. Then we transmit a READ instruction, followed by the 16-bit address we wish to read from, Most Significant Bit first. Next we send a dummy byte to the EEPROM for the purpose of shifting the data out. Finally we pull the SLAVESELECT line high again to release the device after reading one byte, and return the data. If we wanted to read multiple bytes at a time we could hold the SLAVESELECT line low while we repeated the [@data = spi_transfer(0xFF);@] up to 128 times for a full page of data.


For easy copy and pasting the full program text of this tutorial is below:
Added lines 223-327:
#define DATAOUT 11//MOSI
#define DATAIN 12//MISO
#define SPICLOCK 13//sck
#define SLAVESELECT 10//ss

//opcodes
#define WREN 6
#define WRDI 4
#define RDSR 5
#define WRSR 1
#define READ 3
#define WRITE 2

byte eeprom_output_data;
byte eeprom_input_data=0;
byte clr;
int address=0;
//data buffer
char buffer [128];

void fill_buffer()
{
for (int I=0;I<128;I++)
{
buffer[I]=I;
}
}

char spi_transfer(volatile char data)
{
SPDR = data; // Start the transmission
while (!(SPSR & (1<<SPIF))) // Wait the end of the transmission
{
};
return SPDR; // return the received byte
}

void setup()
{
Serial.begin(9600);

pinMode(DATAOUT, OUTPUT);
pinMode(DATAIN, INPUT);
pinMode(SPICLOCK,OUTPUT);
pinMode(SLAVESELECT,OUTPUT);
digitalWrite(SLAVESELECT,HIGH); //disable device
// SPCR = 01010000
//interrupt disabled,spi enabled,msb 1st,master,clk low when idle,
//sample on leading edge of clk,system clock/4 rate (fastest)
SPCR = (1<<SPE)|(1<<MSTR);
clr=SPSR;
clr=SPDR;
delay(10);
//fill buffer with data
fill_buffer();
//fill eeprom w/ buffer
digitalWrite(SLAVESELECT,LOW);
spi_transfer(WREN); //write enable
digitalWrite(SLAVESELECT,HIGH);
delay(10);
digitalWrite(SLAVESELECT,LOW);
spi_transfer(WRITE); //write instruction
address=0;
spi_transfer((char)(address>>8)); //send MSByte address first
spi_transfer((char)(address)); //send LSByte address
//write 128 bytes
for (int I=0;I<128;I++)
{
spi_transfer(buffer[I]); //write data byte
}
digitalWrite(SLAVESELECT,HIGH); //release chip
//wait for eeprom to finish writing
delay(3000);
Serial.print('h',BYTE);
Serial.print('i',BYTE);
Serial.print('\n',BYTE);//debug
delay(1000);
}

byte read_eeprom(int EEPROM_address)
{
//READ EEPROM
int data;
digitalWrite(SLAVESELECT,LOW);
spi_transfer(READ); //transmit read opcode
spi_transfer((char)(EEPROM_address>>8)); //send MSByte address first
spi_transfer((char)(EEPROM_address)); //send LSByte address
data = spi_transfer(0xFF); //get data byte
digitalWrite(SLAVESELECT,HIGH); //release chip, signal end transfer
return data;
}

void loop()
{
eeprom_output_data = read_eeprom(address);
Serial.print(eeprom_output_data,DEC);
Serial.print('\n',BYTE);
address++;
if (address == 128)
address = 0;
delay(500); //pause for readability
}
@]

[@
August 30, 2006, at 05:57 PM by Heather Dewey-Hagborg -
Changed lines 53-54 from:
Once you have your SPI Control Register set correctly you just need to figure out how long you need to pause between instructions and you are ready to go. Now that you have a feel for how SPI works, let's take a look at the EEPROM chip.
to:
Once you have your SPI Control Register set correctly you just need to figure out how long you need to pause between instructions and you are ready to go. Now that you have a feel for how SPI works, let's take a look at the details of the EEPROM chip.
Changed lines 62-63 from:
The device is enabled by pulling the Chip Select (CS) pin low. Instructions are 8 bit opcodes and are shifted in on the rising edge of the data clock. It takes the EEPROM about 10 milliseconds to write a page (128 bytes) of data, so a 10ms pause should follow each EEPROM write routine.
to:
The device is enabled by pulling the Chip Select (CS) pin low. Instructions are sent as 8 bit operational codes (opcodes) and are shifted in on the rising edge of the data clock. It takes the EEPROM about 10 milliseconds to write a page (128 bytes) of data, so a 10ms pause should follow each EEPROM write routine.
Changed lines 127-128 from:
This function loads the output data into the data transmission register, thus starting the SPI transmission. It polls a bit to the SPI Status register (SPSR) to detect when the transmission is complete. It then returns any data that has been shifted in to the data register by the EEPROM.
to:
This function loads the output data into the data transmission register, thus starting the SPI transmission. It polls a bit to the SPI Status register (SPSR) to detect when the transmission is complete using a bit mask, SPIF. An explanation of bit masks can be found [[http://www.arduino.cc/en/Tutorial/BitMask | here]]. It then returns any data that has been shifted in to the data register by the EEPROM.
Changed lines 154-155 from:
After setting our control register up we clear any spurious data from the Status and Control registers.
to:
After setting our control register up we read the SPI status register (SPSR) and data register (SPDR) in to the junk clr variabl to clear out any spurious data from past runs.
August 30, 2006, at 05:51 PM by Heather Dewey-Hagborg -
Changed lines 53-54 from:
Once you have your SPI Control Register set correctly you just need to figure out how long you need to pause between instructions and you are ready to go.
to:
Once you have your SPI Control Register set correctly you just need to figure out how long you need to pause between instructions and you are ready to go. Now that you have a feel for how SPI works, let's take a look at the EEPROM chip.
August 30, 2006, at 05:44 PM by Heather Dewey-Hagborg -
Changed lines 24-32 from:
All SPI settings are determined by the Arduino SPI Control Register (SPCR). The SPCR has 8 bits each of which control a particular SPI setting.
to:
All SPI settings are determined by the Arduino SPI Control Register (SPCR). A register is just a byte of microcontroller memory that can be read from or written to. Registers generally serve three purposes, control, data and status.

Control registers code control settings for various microcontroller functionalities. Usually each bit in a control register effects a particular setting, such as speed or polarity.

Data registers simply hold bytes. For example, the SPI data register (SPDR) holds the byte which is about to be shifted out the MOSI line, and the data which has just been shifted in the MISO line.

Status registers change their state based on various microcontroller conditions. For example, the seventh bit of the SPI status register (SPSR) gets set to 1 when a value is shifted in or out of the SPI.

The SPI control register (SPCR) has 8 bits, each of which control a particular SPI setting.
Changed lines 48-52 from:
-Is data shifted in MSB or LSB first?
-Is the data clock idle when high or low?
-Are samples on the rising or falling edge of clock pulses?
-What speed is the SPI running at?
to:
*Is data shifted in MSB or LSB first?
*Is the data clock idle when high or low?
*Are samples on the rising or falling edge of clock pulses?
*What speed is the SPI running at?
August 30, 2006, at 04:58 PM by Tom Igoe -
Changed lines 14-15 from:
Serial Peripheral Interface (SPI) is a synchronous serial data protocol used by Microcontrollers for communicating with one or more peripheral devices quickly over short distances. It can also be used for communication between two microcontrollers. With an SPI connection there is always one master device (usually a microcontroller) which controls the peripheral devices. Typically there are three lines common to all the devices, Master In Slave Out (MISO) - The Master line for sending data to the peripherals, Master Out Slave In (MOSI) - The Slave line for sending data to the master, and Serial Clock (SCK) - The clock pulses which synchronize data transmission generated by the master. Additionally there is generally a Slave Select pin allocated on each device which the master can use to enable and disable specific devices and avoid false transmissions due to line noise.
to:
Serial Peripheral Interface (SPI) is a synchronous serial data protocol used by Microcontrollers for communicating with one or more peripheral devices quickly over short distances. It can also be used for communication between two microcontrollers.

With an SPI connection there is always one master device (usually a microcontroller) which controls the peripheral devices. Typically there are three lines common to all the devices,
* Master In Slave Out (MISO) - The Master line for sending data to the peripherals,
* Master Out Slave In (MOSI) - The Slave line for sending data to the master,
* Serial Clock (SCK) - The clock pulses which synchronize data transmission generated by the master, and
* Slave Select pin - allocated on each device which the master can use to enable and disable specific devices and avoid false transmissions due to line noise.
August 30, 2006, at 01:51 AM by Heather Dewey-Hagborg -
Added lines 46-49:
The AT25HP512 is a 65,536 byte serial EEPROM. It supports SPI modes 0 and 3, runs at up to 10MHz at 5v and can run at slower speeds down to 1.8v. It's memory is organized as 512 pages of 128 bytes each. It can only be written 128 bytes at a time, but it can be read 1-128 bytes at a time. The device also offers various degerees of write protection and a hold pin, but we won't be covering those in this tutorial.

The device is enabled by pulling the Chip Select (CS) pin low. Instructions are 8 bit opcodes and are shifted in on the rising edge of the data clock. It takes the EEPROM about 10 milliseconds to write a page (128 bytes) of data, so a 10ms pause should follow each EEPROM write routine.
August 30, 2006, at 12:46 AM by Heather Dewey-Hagborg -
Changed lines 16-17 from:
The difficult part about SPI is that the standard is loose and each device implements it a little differently. Generally speaking there are three modes of transmission numbered 0 - 3. These modes control whether data is shifted in and out on the rising or falling edge of the data clock signal, and whether the clock is idle when high or low.
to:
The difficult part about SPI is that the standard is loose and each device implements it a little differently. This means you have to pay special attention to the datasheet when writing your interface code. Generally speaking there are three modes of transmission numbered 0 - 3. These modes control whether data is shifted in and out on the rising or falling edge of the data clock signal, and whether the clock is idle when high or low.
Changed lines 33-35 from:
The eighth bit sets the SPI interrupt, the seventh bit enables the SPI, the sixth bit chooses transmission with the most significant bit going first or Least Significant, the fifth bit puts the Arduino in Master mode, the fourth bit sets the data clock idle when it is low, the third bit sets the SPI to sample data on the rising edge of the data clock, and the second and first bits set the speed of the SPI to system speed / 4 (the fastest).

to:
This means that to write code for a new SPI device you need to note several things and set the SPCR accordingly:
-Is data shifted in MSB or LSB first?
-Is the data clock idle when high or low?
-Are samples on the rising or falling edge of clock pulses?
-What speed is the SPI running at?

Once you have your SPI Control Register set correctly you just need to figure out how long you need to pause between instructions and you are ready to go.
August 29, 2006, at 11:07 PM by Heather Dewey-Hagborg -
Changed lines 14-15 from:
Serial Peripheral Interface (SPI) is a synchronous serial data protocol used by Microcontrollers for communicating with peripheral devices quickly over short distances. It can also be used for communication between two microcontrollers. With an SPI connection
to:
Serial Peripheral Interface (SPI) is a synchronous serial data protocol used by Microcontrollers for communicating with one or more peripheral devices quickly over short distances. It can also be used for communication between two microcontrollers. With an SPI connection there is always one master device (usually a microcontroller) which controls the peripheral devices. Typically there are three lines common to all the devices, Master In Slave Out (MISO) - The Master line for sending data to the peripherals, Master Out Slave In (MOSI) - The Slave line for sending data to the master, and Serial Clock (SCK) - The clock pulses which synchronize data transmission generated by the master. Additionally there is generally a Slave Select pin allocated on each device which the master can use to enable and disable specific devices and avoid false transmissions due to line noise.

The difficult part about SPI is that the standard is loose and each device implements it a little differently. Generally speaking there are three modes of transmission numbered 0 - 3. These modes control whether data is shifted in and out on the rising or falling edge of the data clock signal, and whether the clock is idle when high or low.

All SPI settings are determined by the Arduino SPI Control Register (SPCR). The SPCR has 8 bits each of which control a particular SPI setting.
[@
SPCR
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| SPIE | SPE | DORD | MSTR | CPOL | CPHA | SPR1 | SPR0 |

SPIE - Enables the SPI interrupt when 1
SPE - Enables the SPI when 1
DORD - Sends data least Significant Bit First when 1, most Significant Bit first when 0
MSTR - Sets the Arduino in master mode when 1, slave mode when 0
CPOL - Sets the data clock to be idle when high if set to 1, idle when low if set to 0
CPHA - Samples data on the falling edge of the data clock when 1, rising edge when 0
SPR1 and SPR0 - Sets the SPI speed, 00 is fastest (4MHz) 11 is slowest (250KHz)
@]

The eighth bit sets the SPI interrupt, the seventh bit enables the SPI, the sixth bit chooses transmission with the most significant bit going first or Least Significant, the fifth bit puts the Arduino in Master mode, the fourth bit sets the data clock idle when it is low, the third bit sets the SPI to sample data on the rising edge of the data clock, and the second and first bits set the speed of the SPI to system speed / 4 (the fastest).

August 29, 2006, at 09:56 PM by Heather Dewey-Hagborg -
Added lines 14-15:
Serial Peripheral Interface (SPI) is a synchronous serial data protocol used by Microcontrollers for communicating with peripheral devices quickly over short distances. It can also be used for communication between two microcontrollers. With an SPI connection
August 29, 2006, at 09:45 PM by Heather Dewey-Hagborg -
Changed lines 33-34 from:
[@#define DATAOUT 11//MOSI
to:
[@
#define DATAOUT 11//MOSI
Changed lines 51-52 from:
[@byte eeprom_output_data;
to:
[@
byte eeprom_output_data;
Changed lines 61-62 from:
[@void fill_buffer()
to:
[@
void fill_buffer()
Changed lines 72-73 from:
[@char spi_transfer(volatile char data)
to:
[@
char spi_transfer(volatile char data)
Changed lines 86-87 from:
[@void setup()
to:
[@
void setup()
Changed lines 99-100 from:
[@ // SPCR = 01010000
to:
[@
// SPCR = 01010000
Changed lines 111-112 from:
[@//fill buffer with data
to:
[@
//fill buffer with data
Changed lines 121-122 from:
[@delay(10);
to:
[@
delay(10);
Changed lines 139-140 from:
[@Serial.print('h',BYTE);
to:
[@
Serial.print('h',BYTE);
Changed lines 147-148 from:
[@byte read_eeprom(int EEPROM_address)
to:
[@
byte read_eeprom(int EEPROM_address)
Changed lines 163-164 from:
[@void loop()
to:
[@
void loop()
Changed lines 178-179 from:
[@#define DATAOUT 11//MOSI
to:
[@
#define DATAOUT 11//MOSI
August 29, 2006, at 09:43 PM by Heather Dewey-Hagborg -
Changed lines 162-164 from:
Finally we get to our main loop, the simplest function in the program! Here we just read one byte at a time from the EEPROM and print it out the serial port plus a line feed and a pause for readability. Each time through the loop we increment the eeprom address to read. When the address increments to 128 we turn it back to 0 since we have only filled 128 addresses in the EEPROM with data.

to:
Finally we get to our main loop, the simplest function in the program! Here we just read one byte at a time from the EEPROM and print it out the serial port. We add a line feed and a pause for readability. Each time through the loop we increment the eeprom address to read. When the address increments to 128 we turn it back to 0 because we have only filled 128 addresses in the EEPROM with data.

August 29, 2006, at 09:42 PM by Heather Dewey-Hagborg -
Added lines 59-164:
[@void fill_buffer()
{
for (int I=0;I<128;I++)
{
buffer[I]=I;
}
} @]

This function simply fills our data array with numbers 0 - 127 for each index in the array. This function could easily be changed to fill the array with data relevant to your application.

[@char spi_transfer(volatile char data)
{
SPDR = data; // Start the transmission
while (!(SPSR & (1<<SPIF))) // Wait for the end of the transmission
{
};
return SPDR; // return the received byte
}@]

This function loads the output data into the data transmission register, thus starting the SPI transmission. It polls a bit to the SPI Status register (SPSR) to detect when the transmission is complete. It then returns any data that has been shifted in to the data register by the EEPROM.

The following setup function is long so we will take it in parts.

[@void setup()
{
Serial.begin(9600);

pinMode(DATAOUT, OUTPUT);
pinMode(DATAIN, INPUT);
pinMode(SPICLOCK,OUTPUT);
pinMode(SLAVESELECT,OUTPUT);
digitalWrite(SLAVESELECT,HIGH); //disable device @]

First we initialize our serial connection, set our input and output pin modes and set the SLAVESELECT line high to start. This deselects the device and avoids any false transmission messages due to line noise.

[@ // SPCR = 01010000
//interrupt disabled,spi enabled,msb 1st,master,clk low when idle,
//sample on leading edge of clk,system clock/4 rate (fastest)
SPCR = (1<<SPE)|(1<<MSTR);
clr=SPSR;
clr=SPDR;
delay(10); @]

Now we set the SPI Control register (SPCR) to the binary value 01010000. In the control register each bit sets a different functionality. The eighth bit disables the SPI interrupt, the seventh bit enables the SPI, the sixth bit chooses transmission with the most significant bit going first, the fifth bit puts the Arduino in Master mode, the fourth bit sets the data clock idle when it is low, the third bit sets the SPI to sample data on the rising edge of the data clock, and the second and first bits set the speed of the SPI to system speed / 4 (the fastest).
After setting our control register up we clear any spurious data from the Status and Control registers.

[@//fill buffer with data
fill_buffer();
//fill eeprom w/ buffer
digitalWrite(SLAVESELECT,LOW);
spi_transfer(WREN); //write enable
digitalWrite(SLAVESELECT,HIGH);@]

Here we fill our data array with numbers and send a write enable instruction to the EEPROM. The EEPROM MUST be write enabled before every write instruction. To send the instruction we pull the SLAVESELECT line low, enabling the device, and then send the instruction using the spi_transfer function. Note that we use the WREN opcode we defined at the beginning of the program. Finally we pull the SLAVESELECT line high again to release it.

[@delay(10);
digitalWrite(SLAVESELECT,LOW);
spi_transfer(WRITE); //write instruction
address=0;
spi_transfer((char)(address>>8)); //send MSByte address first
spi_transfer((char)(address)); //send LSByte address
//write 128 bytes
for (int I=0;I<128;I++)
{
spi_transfer(buffer[I]); //write data byte
}
digitalWrite(SLAVESELECT,HIGH); //release chip
//wait for eeprom to finish writing
delay(3000); @]

Now we pull the SLAVESELECT line low to select the device again after a brief delay. We send a WRITE instruction to tell the EEPROM we will be sending data to record into memory. We send the 16 bit address to begin writing at in two bytes, Most Significant Bit first. Next we send our 128 bytes of data from our buffer array, one byte after another without pause. Finally we set the SLAVESELECT pin high to release the device and pause to allow the EEPROM to write the data.

[@Serial.print('h',BYTE);
Serial.print('i',BYTE);
Serial.print('\n',BYTE);//debug
delay(1000);@]

We end the setup function by sending the word "hi" plus a line feed out the built in serial port for debugging purposes. This way if our data comes out looking funny later on we can tell it isn't just the serial port acting up.

[@byte read_eeprom(int EEPROM_address)
{
//READ EEPROM
int data;
digitalWrite(SLAVESELECT,LOW);
spi_transfer(READ); //transmit read opcode
spi_transfer((char)(EEPROM_address>>8)); //send MSByte address first
spi_transfer((char)(EEPROM_address)); //send LSByte address
data = spi_transfer(0xFF); //get data byte
digitalWrite(SLAVESELECT,HIGH); //release chip, signal end transfer
return data;
} @]

This function allows us to read data back out of the EEPROM. First we set the SLAVESELECT line low to enable the device. Then we transmit a READ instruction, followed by the 16-bit address we wish to read from, Most Significant Bit first. Next we send a dummy byte to the EEPROM for the purpose of shifting the data out. Finally we pull the SLAVESELECT line high again to release the device after reading one byte, and return the data. If we wanted to read multiple bytes at a time we could hold the SLAVESELECT line low while we repeated the [@data = spi_transfer(0xFF);@] up to 128 times for a full page of data.

[@void loop()
{
eeprom_output_data = read_eeprom(address);
Serial.print(eeprom_output_data,DEC);
Serial.print('\n',BYTE);
address++;
delay(500); //pause for readability
} @]

Finally we get to our main loop, the simplest function in the program! Here we just read one byte at a time from the EEPROM and print it out the serial port plus a line feed and a pause for readability. Each time through the loop we increment the eeprom address to read. When the address increments to 128 we turn it back to 0 since we have only filled 128 addresses in the EEPROM with data.

Added lines 166-270:

[@#define DATAOUT 11//MOSI
#define DATAIN 12//MISO
#define SPICLOCK 13//sck
#define SLAVESELECT 10//ss

//opcodes
#define WREN 6
#define WRDI 4
#define RDSR 5
#define WRSR 1
#define READ 3
#define WRITE 2

byte eeprom_output_data;
byte eeprom_input_data=0;
byte clr;
int address=0;
//data buffer
char buffer [128];

void fill_buffer()
{
for (int I=0;I<128;I++)
{
buffer[I]=I;
}
}

char spi_transfer(volatile char data)
{
SPDR = data; // Start the transmission
while (!(SPSR & (1<<SPIF))) // Wait the end of the transmission
{
};
return SPDR; // return the received byte
}

void setup()
{
Serial.begin(9600);

pinMode(DATAOUT, OUTPUT);
pinMode(DATAIN, INPUT);
pinMode(SPICLOCK,OUTPUT);
pinMode(SLAVESELECT,OUTPUT);
digitalWrite(SLAVESELECT,HIGH); //disable device
// SPCR = 01010000
//interrupt disabled,spi enabled,msb 1st,master,clk low when idle,
//sample on leading edge of clk,system clock/4 rate (fastest)
SPCR = (1<<SPE)|(1<<MSTR);
clr=SPSR;
clr=SPDR;
delay(10);
//fill buffer with data
fill_buffer();
//fill eeprom w/ buffer
digitalWrite(SLAVESELECT,LOW);
spi_transfer(WREN); //write enable
digitalWrite(SLAVESELECT,HIGH);
delay(10);
digitalWrite(SLAVESELECT,LOW);
spi_transfer(WRITE); //write instruction
address=0;
spi_transfer((char)(address>>8)); //send MSByte address first
spi_transfer((char)(address)); //send LSByte address
//write 128 bytes
for (int I=0;I<128;I++)
{
spi_transfer(buffer[I]); //write data byte
}
digitalWrite(SLAVESELECT,HIGH); //release chip
//wait for eeprom to finish writing
delay(3000);
Serial.print('h',BYTE);
Serial.print('i',BYTE);
Serial.print('\n',BYTE);//debug
delay(1000);
}

byte read_eeprom(int EEPROM_address)
{
//READ EEPROM
int data;
digitalWrite(SLAVESELECT,LOW);
spi_transfer(READ); //transmit read opcode
spi_transfer((char)(EEPROM_address>>8)); //send MSByte address first
spi_transfer((char)(EEPROM_address)); //send LSByte address
data = spi_transfer(0xFF); //get data byte
digitalWrite(SLAVESELECT,HIGH); //release chip, signal end transfer
return data;
}

void loop()
{
eeprom_output_data = read_eeprom(address);
Serial.print(eeprom_output_data,DEC);
Serial.print('\n',BYTE);
address++;
if (address == 128)
address = 0;
delay(500); //pause for readability
}
@]
August 29, 2006, at 08:15 PM by Heather Dewey-Hagborg -
Added lines 30-61:

Now we will write the code to enable SPI communication between the EEPROM and the Arduino. In the setup routine this program fills 128 bytes, or one page of the EEPROM with data. In the main loop it reads that data back out, one byte at a time and prints that byte out the built in serial port. We will walk through the code in small sections.

[@#define DATAOUT 11//MOSI
#define DATAIN 12//MISO
#define SPICLOCK 13//sck
#define SLAVESELECT 10//ss

//opcodes
#define WREN 6
#define WRDI 4
#define RDSR 5
#define WRSR 1
#define READ 3
#define WRITE 2 @]

Here we set up our pre-processor directives. Pre-processor directives are processed before the actual compilation begins. They start with a "#" and do not end with semi-colons.

First we define the pins we will be using for our SPI connection, DATAOUT, DATAIN, SPICLOCK and SLAVESELECT. Then we define our opcodes for the EEPROM. Opcodes are control commands.

[@byte eeprom_output_data;
byte eeprom_input_data=0;
byte clr;
int address=0;
//data buffer
char buffer [128]; @]

Here we allocate the global variables we will be using later in the program. Note [@char buffer [128];@]. this is a 128 byte array we will be using to store the data for the EEPROM write.

For easy copy and pasting the full program text of this tutorial is below:
[@
@]
August 29, 2006, at 07:58 PM by Heather Dewey-Hagborg -
Added lines 21-28:
Insert the AT25HP512 chip into the breadboard. Connect 5V power and ground from the breadboard to 5V power and ground from the microcontroller. Connect EEPROM pins 3, 7 and 8 to 5v and pin 4 to ground.

PICTURE of pwr wires

Connect EEPROM pin 1 to Arduino pin 10 (Slave Select), EEPROM pin 2 to Arduino pin 12 (Master In Slave Out), EEPROM pin 5 to Arduino pin 11 (Master Out Slave In), and EEPROM pin 6 to Arduino pin 13 (Serial Clock).

PICTURE of SPI wires
August 27, 2006, at 08:17 PM by Heather Dewey-Hagborg -
Changed line 1 from:
!Interfacing a serial EEPROM using SPI
to:
!Interfacing a Serial EEPROM Using SPI
Changed lines 12-15 from:
!!Serial Peripheral Interface

!!Atmel 25HP512 EEPROM chip
to:
!!Introduction to the Serial Peripheral Interface

!!Introduction to Serial EEPROM
August 27, 2006, at 08:14 PM by Heather Dewey-Hagborg -
Added lines 14-18:
!!Atmel 25HP512 EEPROM chip

Attach:at25hp512_pins.jpg
Attach:at25hp512_pins2.jpg
August 27, 2006, at 08:11 PM by Heather Dewey-Hagborg -
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to:
(IN PROGRESS)
Added lines 13-16:

!!Prepare the Breadboard

!!Program the Arduino
August 27, 2006, at 08:09 PM by Heather Dewey-Hagborg -
Added lines 1-11:
!Interfacing a serial EEPROM using SPI

In this tutorial you will learn how to interface with an AT25HP512 Atmel serial EEPROM using the Serial Peripheral Interface (SPI) protocol. EEPROM chips such as this are very useful for data storage, and the steps we will cover for implementing SPI communication can be modified for use with most other SPI devices.

Materials Needed:

# AT25HP512 Serial EEPROM chip (or similar)
# Hookup wire
# Arduino Microcontroller Module

!!Serial Peripheral Interface

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