Pic32 spi example

Pic32 spi example


  • Electronic Design Resources
  • SPI Communication with PIC microcontroller
  • PIC32 DMA SPI
  • PIC32 + RTC via SPI doesn’t work
  • SPI Tutorial With PIC Microcontrollers | Serial Peripheral Interface
  • How to Implement SPI Using PIC18F4550
  • Electronic Design Resources

    The SPI protocol was initially developed and proposed by Motorola for use in microprocessor and microcontroller based interface applications. In a system that uses the SPI bus, one device acts as the master and other devices act as slaves. The master initiates a communication and also provides clock pulses to the slave devices.

    This module is built into many different PICmicro devices. SPI is usually called a 4-wire full duplex synchronous serial communication, the functions of the 4 wires are as follow: SCLK Serial Clock : This is the serial clock signal.

    It is generated by the master device and controls when data is sent and when it is read. This signal must be used when more than one slave exists in a system, but can be optional when only one slave exists in the circuit but it always a good practice to use it. Depending on the number of devices in the bus, we can have more than one chip Select lines, one per device in the bus. Figure 1 hows the microcontroller connected to 3 SPI slaves 3 chip select lines. Depending on the number of slave devices connected, the master will have one dedicated pin for SS line for each slave.

    Figure 1 below shows an illustration of one master microcontroller controlling three slave devices. Advantages of SPI: Full duplex communication.

    SPI can operate at extremely high speeds but generally dictated by the slowest device on the bus. Common bus speeds are in the Mbits per second range The hardware protocol is simple to implement, the receiver hardware can be a simple shift register. The Clock Edge: Active to Idle. Clock Edge: Active to Idle. Slave Select pin is enabled. This routine must be called before any other MSSP routine is called. This is a blocking routine. SPI is a data exchange mechanism.

    As one device sends a byte of data, so the other transmits one. If the incoming data is not read, then the data will be lost and the SPI module may become disabled as a result. Always read the data after a transfer has taken place, even if the data has no use in your application. However, each device has two data lines, one for input and one for output. Below is the Master Main.

    SPI Communication with PIC microcontroller

    Which mostly depend on how they are manufactured and how data should be flowing through the network of devices in that particular application. Each device is connected between 2 other devices in a circular Logically way as shown in the diagram down below.

    The SPI port of each slave device is designed to send data out during the second group of clock pulses an exact copy of the data it received during the first group of clock pulses. The whole chain acts as a communication shift register. Each slave copies the input data to the output in the next clock cycle until the SS line goes high.

    Such a feature only requires a single SS line from the master, rather than a separate SS line for each slave. That means a data frame will keep propagating through slave devices as long as the SS line is held low. The following diagram will show you how a single SPI master can address multiple slave devices using only one SS line. Independent Slave In the independent slave configuration, there is an independent slave select line for each slave. This is the way SPI is normally used.

    The master asserts only one chip select at a time. A typical connection diagram for a system with multiple slaves connected in the independent configuration is shown below. Which will require too many IO pins to control all SS lines. Here is a short list for the pros of SPI. Full-Duplex serial communication. Potentially high-speed data transfer rates can be achieved with SPI. Few wires are required for the SPI Bus typically 4 lines. Easy software configuration and setup.

    Extremely flexible data transfer. Very simple hardware structure. Transceivers are not needed unlike CAN. Disadvantages of SPI No hardware slave acknowledgment the master could be transmitting to nowhere without knowing.

    Typically supports only one master device. Requires more pins unlike I2C. No hardware-level error-checking protocol is defined. The SPI mode allows 8 bits of data to be synchronously transmitted and received simultaneously.

    All four modes of SPI are supported. This double-buffering of the received data SSPBUF allows the next byte to start reception before reading the data that was just received. This data may be irrelevant if the SPI is only a transmitter. If the interrupt method is not going to be used, then software polling can be done to ensure that a write collision does not occur.

    For the pins to behave as the serial port function, some must have their data direction bits in the TRISx register appropriately programmed. The master controller Processor 1 initiates the data transfer by sending the SCK signal. Data frame is shifted out of both shift registers on their programmed clock edge and latched on the opposite edge of the clock. Both processors should be programmed to the same Clock Polarity CKP , then both controllers would send and receive data at the same time.

    Whether the data frame is meaningful or dummy data depends on the application software. The master determines when the slave is to broadcast data by the software protocol. As each byte is received, it will be loaded into the SSPBUF register as if a normally received byte interrupts and status bits appropriately set.

    The clock phase and polarity are selected by appropriately programming the control bits. This then would give waveforms for SPI communication as shown in the timings diagram down below.

    PIC32 DMA SPI

    Figure 1 below shows an illustration of one master microcontroller controlling three slave devices.

    PIC32 + RTC via SPI doesn’t work

    Advantages of SPI: Full duplex communication. SPI can operate at extremely high speeds but generally dictated by the slowest device on the bus. Common bus speeds are in the Mbits per second range The hardware protocol is simple to implement, the receiver hardware can be a simple shift register. The Clock Edge: Active to Idle.

    SPI Tutorial With PIC Microcontrollers | Serial Peripheral Interface

    Clock Edge: Active to Idle. Slave Select pin is enabled. This routine must be called before any other MSSP routine is called. Which will require too many IO pins to control all SS lines. Here is a short list for the pros of SPI.

    Full-Duplex serial communication. Potentially high-speed data transfer rates can be achieved with SPI. Few wires are required for the SPI Bus typically 4 lines.

    Easy software configuration and setup.

    How to Implement SPI Using PIC18F4550

    Extremely flexible data transfer. Very simple hardware structure. Transceivers are not needed unlike CAN. Disadvantages of SPI No hardware slave acknowledgment the master could be transmitting to nowhere without knowing. Typically supports only one master device. Requires more pins unlike I2C. No hardware-level error-checking protocol is defined.

    The CKP bit is used to decide which are the idle state and the active state of the clock. Read PIC microcontroller tutorial to know more. To have clear understanding of code writing visit PIC Microcontroller tutorial.

    It also set the clock polarity and when to sample input data and to transmit output data regarding the clock transition states. It also sets the SPI pins as input or output as required by the master. It can also disable all other modules multiplexed into the SPI pins. It also sets the SPI pins as input or output as required by the slave. The master first write the data and then wait for the data to complete transmission and then read the received data while the slave first wait till all the data bits has been received, and then reads the data followed by a data write.

    The functions are explained with more details in PIC microcontroller tutorial.


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