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. 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,.
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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. 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,. 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.
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. Status registers change their state based on various microcontroller conditions. 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. It's memory is organized as pages of bytes each. It can only be written bytes at a time, but it can be read 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 sent as 8 bit operational codes opcodes and are shifted in on the rising edge of the data clock. Insert the AT25HP chip into the breadboard. Connect 5V power and ground from the breadboard to 5V power and ground from the microcontroller. 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. 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. Opcodes are control commands:. Here we allocate the global variables we will be using later in the program.
Note char buffer ;. This deselects the device and avoids any false transmission messages due to line noise:. In the control register each bit sets a different functionality. Note that we use the WREN opcode we defined at the beginning of the program. We send the 16 bit address to begin writing at in two bytes, Most Significant Bit first. Next we send our bytes of data from our buffer array, one byte after another without pause.
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:. 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 we turn it back to 0 because we have only filled addresses in the EEPROM with data:.
This function could easily be changed to fill the array with data relevant to your application:. An explanation of bit masks can be found here.
RS Stock No. Product Details. Maximum Operating Temperature. Minimum Operating Supply Voltage. Minimum Operating Temperature.
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The Microchip Technology Inc. Interface SPI compatible serial bus. The bus signals. SI and data out SO lines. Access to the device is. There are two other inputs that provide the end user.
25LC320 32K2.5VSPIBusSerialEEPROM. Datasheet pdf. Equivalent