- BEST SERIAL COMMUNICATION PROTOCOL BETWEEN ARDUINOS HOW TO
- BEST SERIAL COMMUNICATION PROTOCOL BETWEEN ARDUINOS CODE
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. Instructions are sent as 8 bit operational codes (opcodes) and are shifted in on the rising edge of the data clock. The device is enabled by pulling the Chip Select (CS) pin low. The device also offers various degerees of write protection and a hold pin, but we won't be covering those in this tutorial. It can only be written 128 bytes at a time, but it can be read 1-128 bytes at a time. It's memory is organized as 512 pages of 128 bytes each. It supports SPI modes 0 and 3, runs at up to 10MHz at 5v and can run at slower speeds down to 1.8v. The AT25HP512 is a 65,536 byte serial EEPROM. Now that you have a feel for how SPI works, let's take a look at the details of the EEPROM chip. 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.
BEST SERIAL COMMUNICATION PROTOCOL BETWEEN ARDUINOS CODE
This means that to write code for a new SPI device you need to note several things and set the SPCR accordingly:Īre samples on the rising or falling edge of clock pulses? The SPI control register (SPCR) has 8 bits, each of which control a particular SPI setting.ġ7 SPR1 and SPR0 - Sets the SPI speed, 00 is fastest ( 4 MHz ) 11 is slowest ( 250 KHz ) 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. Status registers change their state based on various microcontroller conditions. 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. Usually each bit in a control register effects a particular setting, such as speed or polarity.ĭata registers simply hold bytes. Registers generally serve three purposes, control, data and status.Ĭontrol registers code control settings for various microcontroller functionalities. A register is just a byte of microcontroller memory that can be read from or written to. 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.Īll SPI settings are determined by the Arduino SPI Control Register (SPCR). Generally speaking there are three modes of transmission numbered 0 - 3. This means you have to pay special attention to the datasheet when writing your interface code. The difficult part about SPI is that the standard is loose and each device implements it a little differently. See the table below to understand the new terminology: Master/Slave (OLD) Arduino no longer supports the use of this terminology. Serial Clock (SCK) - The clock pulses which synchronize data transmission generated by the Controller, andĬhip Select pin (CS) - allocated on each device which the Controller can use to enable and disable specific devices and avoid false transmissions due to line noise.Ĭontroller/peripheral is formerly known as master/slave. Typically there are three lines common to all the devices:Ĭontroller In, Peripheral Out (CIPO) - The Peripheral line for sending data to the Controller,Ĭontroller Out Peripheral In (COPI) - The Controller line for sending data to the Peripherals,
With an SPI connection there is always one Controller device (usually a microcontroller) which controls the peripheral devices. It can also be used for communication between two microcontrollers. 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. Arduino Microcontroller ( Link to store).AT25HP512 Serial EEPROM chip (or similar).Enable SPI communication between an EEPROM chip and the Arduino.
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. 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.
BEST SERIAL COMMUNICATION PROTOCOL BETWEEN ARDUINOS HOW TO
In this tutorial you will learn how to interface with an AT25HP512 Atmel serial EEPROM using the Serial Peripheral Interface (SPI) protocol.