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Multiple slave-devices may be supported through selection with individual chip select (CS), sometimes called slave select (SS) lines. The master (controller) device originates the frame for reading and writing. SPI AND SERIAL COMMUNICATION BASICS FULLSPI devices communicate in full duplex mode using a master-slave architecture usually with a single master (though some Atmel devices support changing roles on the fly depending on an external (SS) pin). Typical applications include Secure Digital cards and liquid crystal displays. The interface was developed by Motorola in the mid-1980s and has become a de facto standard. The Serial Peripheral Interface ( SPI) is a synchronous serial communication interface specification used for short-distance communication, primarily in embedded systems. *please note this library is far from perfect, it needs improvment.Synchronous serial communication interface SPI bus Type If you have any questions/comments or suggestions send me an email at Good Luck and happy coding The library included is taken from the data sheet. SPI AND SERIAL COMMUNICATION BASICS HOW TOThis covers how to send and receive signals via SPI. SPI AND SERIAL COMMUNICATION BASICS CODEArduino Code & Atmega PDFs o Arduino Test Code o ATMEL SPI Communications o Atmega DatasheetĪfter you are done loading the test code i recommend giving chapter 18(Pg 166) on the data sheet a good read. The following code below will set the device to output its lowest resistance and then send the value 170 which should result in an output of 3.3volts. 0 represents the highest pot value, 255 being the lowest (1-2) ohm. The potentiometer selector bits are self-explanatory.įor the pot values (data byte) we can write 0-255. ![]() Bits 1-0: 00: Dummy code 01: Command executed on pot 0 10: Command executed on pot 1 11: Command executed on both pot 0 & 1 Command Byte:īits 6-5: 00 & 11: useless commands nothing will occur using these two commandsĠ1: write data to the selected potentiometer.10: Shutdown the selected potentiometer (when in shutdown mode pot defaults to its highest resistance value). Sending 0x13 will work as well however if you have the dual package it will address both pots. This will allow me to write to the device and control pot0 Below is an excerpt from the datasheet pay close attention to the values.įor my experiment I am only using 1 device and I want to write data to it. We can only send one 8bit command at a time, notice on the data sheet that before we transfer the pot value of 0-255 we are required to send a command byte (Pg 18). To write from pin 11 to the device we will need to use the command: SPI.setBitOrder(MSBFIRST) // sets the data sent from the Arduino is MSB first. SPI.begin() // starts the SPI predefined program written in the spi.h library Since the chip I am using reads data in MSB (most significant byte first).To enable the SPI module we will need to send the following commands. We still however need to declaire the bit order and tell the Arduino to begin spi data write. Using the library is nice as it handles most of the work in the background. ![]() For the first portion of this experiment we will be using the ARDUINO IDE this will make understanding concepts easier. The voltage between the wiper and the gnd pin. However for this experiment I chose to calc You can short the pins PB0 & PW0 to make a resistor and connect a multimeter to pins PW0 and PA0. Anything inbetween is ignored.įor the Arduino (atmega328p) we will be using the IDE library. When the Enable (CS,SS) pin is pulled low the MCP4101 device accepts the
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