Basics of the SPI Communication Protocol. When you connect a microcontroller to a sensor, display, or other module, do you ever think about how the two devices talk to each other What exactly are they saying How are they able to understand each otherCommunication between electronic devices is like communication between humans. Both sides need to speak the same language. In electronics, these languages are called communication protocols. Luckily for us, there are only a few communication protocols we need to know when building most DIY electronics projects. In this series of articles, we will discuss the basics of the three most common protocols Serial Peripheral Interface SPI, Inter Integrated Circuit I2. C, and Universal Asynchronous ReceiverTransmitter UART driven communication. First, well begin with some basic concepts about electronic communication, then explain in detail how SPI works. In the next article, well discuss UART driven communication, and in the third article, well dive into I2. In radio communications, a radio receiver radio is an electronic device that receives radio waves and converts the information carried by them to a usable form. USA. com provides easy to find states, metro areas, counties, cities, zip codes, and area codes information, including population, races, income, housing, school. C. SPI, I2. C, and UART are quite a bit slower than protocols like USB, ethernet, Bluetooth, and Wi. Fi, but theyre a lot more simple and use less hardware and system resources. SPI, I2. C, and UART are ideal for communication between microcontrollers and between microcontrollers and sensors where large amounts of high speed data dont need to be transferred. Serial vs. Parallel Communication. Electronic devices talk to each other by sending bits of data through wires physically connected between devices. A bit is like a letter in a word, except instead of the 2. English alphabet, a bit is binary and can only be a 1 or 0. Bits are transferred from one device to another by quick changes in voltage. In a system operating at 5 V, a 0 bit is communicated as a short pulse of 0 V, and a 1 bit is communicated by a short pulse of 5 V. The bits of data can be transmitted either in parallel or serial form. In parallel communication, the bits of data are sent all at the same time, each through a separate wire. The following diagram shows the parallel transmission of the letter C in binary 0. Bullies can make our lives difficult at any ageeven when youre an adultbut you dont have to sit by and take undeserved punishment from someone bigger. In serial communication, the bits are sent one by one through a single wire. The following diagram shows the serial transmission of the letter C in binary 0. Wifi Signal Receiver Circuit Diagram' title='Wifi Signal Receiver Circuit Diagram' />Introduction to SPI Communication. SPI is a common communication protocol used by many different devices. For example, SD card modules, RFID card reader modules, and 2. GHz wireless transmitterreceivers all use SPI to communicate with microcontrollers. One unique benefit of SPI is the fact that data can be transferred without interruption. Any number of bits can be sent or received in a continuous stream. With I2. C and UART, data is sent in packets, limited to a specific number of bits. Start and stop conditions define the beginning and end of each packet, so the data is interrupted during transmission. Devices communicating via SPI are in a master slave relationship. Search Pdf Sharepoint Foundation 2010. The master is the controlling device usually a microcontroller, while the slave usually a sensor, display, or memory chip takes instruction from the master. Languard Network Scanner Serial. The simplest configuration of SPI is a single master, single slave system, but one master can control more than one slave more on this below. MOSI Master OutputSlave Input  Line for the master to send data to the slave. MISO Master InputSlave Output  Line for the slave to send data to the master. SCLK Clock  Line for the clock signal. SSCS Slave SelectChip Select  Line for the master to select which slave to send data to. In practice, the number of slaves is limited by the load capacitance of the system, which reduces the ability of the master to accurately switch between voltage levels. How SPI Works. The Clock. The clock signal synchronizes the output of data bits from the master to the sampling of bits by the slave. One bit of data is transferred in each clock cycle, so the speed of data transfer is determined by the frequency of the clock signal. SPI communication is always initiated by the master since the master configures and generates the clock signal. Any communication protocol where devices share a clock signal is known as synchronous. SPI is a synchronous communication protocol. There are also asynchronous methods that dont use a clock signal. For example, in UART communication, both sides are set to a pre configured baud rate that dictates the speed and timing of data transmission. The clock signal in SPI can be modified using the properties of clock polarity and clock phase. These two properties work together to define when the bits are output and when they are sampled. Clock polarity can be set by the master to allow for bits to be output and sampled on either the rising or falling edge of the clock cycle. Clock phase can be set for output and sampling to occur on either the first edge or second edge of the clock cycle, regardless of whether it is rising or falling. Slave Select. The master can choose which slave it wants to talk to by setting the slaves CSSS line to a low voltage level. In the idle, non transmitting state, the slave select line is kept at a high voltage level. Multiple CSSS pins may be available on the master, which allows for multiple slaves to be wired in parallel. If only one CSSS pin is present, multiple slaves can be wired to the master by daisy chaining. Multiple Slaves. SPI can be set up to operate with a single master and a single slave, and it can be set up with multiple slaves controlled by a single master. There are two ways to connect multiple slaves to the master. If the master has multiple slave select pins, the slaves can be wired in parallel like this If only one slave select pin is available, the slaves can be daisy chained like this MOSI and MISOThe master sends data to the slave bit by bit, in serial through the MOSI line. The slave receives the data sent from the master at the MOSI pin. Data sent from the master to the slave is usually sent with the most significant bit first. The slave can also send data back to the master through the MISO line in serial. The data sent from the slave back to the master is usually sent with the least significant bit first. Steps of SPI Data Transmission. The master outputs the clock signal 2. The master switches the SSCS pin to a low voltage state, which activates the slave 3. The master sends the data one bit at a time to the slave along the MOSI line. The slave reads the bits as they are received 4. If a response is needed, the slave returns data one bit at a time to the master along the MISO line. The master reads the bits as they are received Advantages and Disadvantages of SPIThere are some advantages and disadvantages to using SPI, and if given the choice between different communication protocols, you should know when to use SPI according to the requirements of your project Advantages. No start and stop bits, so the data can be streamed continuously without interruption. No complicated slave addressing system like I2. CHigher data transfer rate than I2. C almost twice as fastSeparate MISO and MOSI lines, so data can be sent and received at the same time. Disadvantages. Uses four wires I2. C and UARTs use twoNo acknowledgement that the data has been successfully received I2. C has thisNo form of error checking like the parity bit in UARTOnly allows for a single master. Hopefully this article has given you a better understanding of SPI. How to USB remote control receiver. Now that we listen to MP3s, and watch XVIDs or x. Unless you have a special HTPC, though, youre probably stuck using the keyboard to pause, change the volume, and fast forward through annoying Mythbusters recaps. PC remote control receivers range from ancient serial port designs who has one to USB devices not supported by popular software. In this how to we design a USB infrared receiver that imitates a common protocol supported by software for Windows, Linux, and Mac. Weve got a full guide to the protocol plus schematics and a parts list. Design overview. Remote controls transmit data on an modulated infrared beam. An infrared receiver IC separates the modulated beam into a clean stream of 0s and 1s. The data stream is decoded by a microcontroller and sent to a computer over a USB connection. Software processes the codes and triggers actions on the computer. Background. Computer infrared receivers. The oldest PC infrared receiver design uses a receiver IC to toggle a serial port pin, usually DCD. This design probably originated on Usenet, and its still the most popular on the web Engadget, Instructables, etc. These arent true serial devices because they dont send data to the PC. Instead, a computer program times pulses on the serial port and demodulates the signal. This is a super simple design, but it depends on direct interrupt access and timing precision thats no longer available in Windows. Linux or Mac users can try this receiver, if you still have a serial port. We couldnt get this type of receiver to work with the serial port on a modern Windows XP PC, and dont expect the precise timing to transfer through a USB serial converter. Some more advanced infrared receivers are true serial port devices that measure or decoding infrared signals before sending data to the computer. The UIRIRMan and UIR2 incorporate a classic PIC 1. F8. 4, but dont provide firmware andor source code. These devices should work on a modern computer, through a USB serial converter if necessary. The USBTINY and USBIRBOY are native USB devices, but lack wide support. Receiver software. Regardless of receiver type, the computer needs a program to listen for incoming remote commands and convert them to actions on the computer. Linux and Mac users have LIRC, which supports a bunch of different receiver types. Windows users are a bit less fortunate. Win. LIRC is an abandoned Windows port of LIRC for simple interrupt based serial port receivers Win. LIRC was last developed in 2. Girder was originally a freeware PC automation utility, but has become expensive bloatware with a 3. Fortunately, the last freeware version of Girder 3. Working with IR remote protocols. Decoding IR signals. Remote controls encode commands in the spacing or timing of a 3. KHz carrier pulse, San Bergmans has an explanation of the principals involved. An infrared receiver IC separates the data stream from the carrier. Our job is to decode the data stream with a microcontroller. There are dozens of remote control protocols, but Phillips RC5 is widespread and commonly used by hobbyists. RC5 is stream of 1. A pulse during the first half of the bit time represents 0, a pulse in the second half represents 1. This scheme is called Manchester coding. We used a logic analyzer to examine the output of a Happauge Win. TV remote control, a known RC5 remote. The diagram shows two presses of the 1 button, and two presses of the 2 button note that the output is inversed and the Manchester coding is backwards from the above description. The first two bit times are start bits, followed by a toggle bit. The toggle bit inverses each time a button is pressed so the receiver can tell the difference between a hold and a repeated press. The next 5 bits are the address 0b. E, followed by the command 0b. A backwards compatible extension to RC5 uses the second start bit as command bit 7. Representing remote codes to the computer. Looking at previous designs, we saw three general methods of communicating remote commands to a computer Protocol specific receivers decode one protocol, and send actual decoded commands to the PCA more general type of receiver measures the timing and spacing of each pulse and sends the full waveform to the PC for analysis. Some receivers create a unique hash for a signal, but dont actually include enough data to fully recreate the waveform. While our preference is towards the general hash method, our only remote uses RC5 and it was more interesting to build an RC5 specific decoder. We describe modifications for a more general version in the firmware section. Computer interface protocol. We didnt want to write our own receiver software or driver, so we looked for an existing, well established communication protocol to imitate. The UIRIRMANIRACTInfraHollywood type receiver is supported by Girder and LIRC, and uses a simple serial protocol with handshake The device is initialized by the DTS and DTR pins of the serial port. We dont have these and dont care. The computer sends IR, with an optional delay. The device replies OK. Well just send OK on every RRemote control codes are sent as a unique six byte hash. Well decode an RC5 signal and send the actual values, but a generic hash could be used instead. This protocol is for a serial port device, but our USB receiver will appear as a virtual serial port and the program wont know the difference. Hardware. Click here for a full size schematic png. Our receiver is based on a USB enabled PIC 1. F2. 45. 5 microcontroller, the smaller, cheaper version of the 1. F2. 55. 0. The 1. F family is programmable with the hobbyist favorite JDM style programmers if a diode is used to drop VPP to a safe level. The PIC gets one decoupling capacitor C1, and a diode D1 and resistorR1 on the ICSP programming header. We exposed the serial port on a pin header for debugging or a mixed USBserial port version using a MAX RS2. IC. The USB peripheral requires a 2. MHz external clock Q1, C5,6, and a. F capacitor. We faked the capacitor using 2 x. F decoupling capacitors C2,3. A 3mm LED LED1 and a 3. R2 show USB connection status. We used a TSOP 1. IC which calls for a 4. F decoupling capacitor C4. If you cant find this particular IC, any receiver listed here should work. The TSOP 1. 73. 8 output is the inverse of the received signal, it pulls to ground when a pulse is detected, so a pull up resistor R3 holds the pin high when no signal is present. Check if you use a different receiver, you may need to use a pull down resistor and reverse the Manchester decoding routine in the firmware. The circuit draws power from the USB bus, so we dont need an additional power supply. Parts list. Click here for a full size placement diagram png. The PCB design is 1. The schematic and PCB were made with Cadsoft Eagle, freeware versions are available for most platforms. All the files are included in the project archive Firmware. The firmware is written in C using Microchips free demonstration C1. Firmware and source are included in the project archive We used version 2. Microchips USB stack to create a USB serial port using the default drivers already available on most systems. The USB stack has simple functions to enumerate the USB device and transfer data between device and host. It only took a few pin changes to get the CDC demonstration working on our custom hardware.